diff --git a/src/dialogs/certifywidget.cpp b/src/dialogs/certifywidget.cpp
index 109191694..22ce956ba 100644
--- a/src/dialogs/certifywidget.cpp
+++ b/src/dialogs/certifywidget.cpp
@@ -1,793 +1,749 @@
 /*  dialogs/certifywidget.cpp
 
     This file is part of Kleopatra, the KDE keymanager
     SPDX-FileCopyrightText: 2019, 2021 g10 Code GmbH
     SPDX-FileContributor: Ingo Klöcker <dev@ingo-kloecker.de>
 
     SPDX-License-Identifier: GPL-2.0-or-later
 */
 
 #include <config-kleopatra.h>
 
 #include "certifywidget.h"
 
 #include "view/infofield.h"
 #include <utils/accessibility.h>
 #include <utils/expiration.h>
 #include <utils/keys.h>
 
 #include <settings.h>
 
 #include "kleopatra_debug.h"
 
 #include <KConfigGroup>
 #include <KDateComboBox>
 #include <KLocalizedString>
 #include <KMessageBox>
 #include <KMessageWidget>
 #include <KSeparator>
 #include <KSharedConfig>
 
 #include <Libkleo/Algorithm>
 #include <Libkleo/DefaultKeyFilter>
 #include <Libkleo/Formatting>
 #include <Libkleo/KeyCache>
 #include <Libkleo/KeySelectionCombo>
+#include <Libkleo/NavigatableTreeWidget>
 #include <Libkleo/Predicates>
 
 #include <QGpgME/ChangeOwnerTrustJob>
 #include <QGpgME/Protocol>
 
 #include <QAction>
 #include <QCheckBox>
 #include <QHBoxLayout>
 #include <QIcon>
 #include <QLabel>
 #include <QLineEdit>
-#include <QListView>
 #include <QParallelAnimationGroup>
 #include <QPropertyAnimation>
 #include <QPushButton>
 #include <QScrollArea>
-#include <QStandardItemModel>
 #include <QToolButton>
 #include <QVBoxLayout>
 
 #include <gpgme++/key.h>
 
+Q_DECLARE_METATYPE(GpgME::UserID)
+
 using namespace Kleo;
+using namespace GpgME;
 
 static QDebug operator<<(QDebug s, const GpgME::UserID &userID)
 {
     return s << Formatting::prettyUserID(userID);
 }
 
 namespace
 {
 
 // Maybe move this in its own file
 // based on code from StackOverflow
 class AnimatedExpander : public QWidget
 {
     Q_OBJECT
 public:
     explicit AnimatedExpander(const QString &title, const QString &accessibleTitle = {}, QWidget *parent = nullptr);
     void setContentLayout(QLayout *contentLayout);
 
 private:
     QGridLayout mainLayout;
     QToolButton toggleButton;
     QFrame headerLine;
     QParallelAnimationGroup toggleAnimation;
     QWidget contentArea;
     int animationDuration{300};
 };
 
 AnimatedExpander::AnimatedExpander(const QString &title, const QString &accessibleTitle, QWidget *parent)
     : QWidget{parent}
 {
 #ifdef Q_OS_WIN
     // draw dotted focus frame if button has focus; otherwise, draw invisible frame using background color
     toggleButton.setStyleSheet(
         QStringLiteral("QToolButton { border: 1px solid palette(window); }"
                        "QToolButton:focus { border: 1px dotted palette(window-text); }"));
 #else
     // this works with Breeze style because Breeze draws the focus frame when drawing CE_ToolButtonLabel
     // while the Windows styles (and Qt's common base style) draw the focus frame before drawing CE_ToolButtonLabel
     toggleButton.setStyleSheet(QStringLiteral("QToolButton { border: none; }"));
 #endif
     toggleButton.setToolButtonStyle(Qt::ToolButtonTextBesideIcon);
     toggleButton.setArrowType(Qt::ArrowType::RightArrow);
     toggleButton.setText(title);
     if (!accessibleTitle.isEmpty()) {
         toggleButton.setAccessibleName(accessibleTitle);
     }
     toggleButton.setCheckable(true);
     toggleButton.setChecked(false);
 
     headerLine.setFrameShape(QFrame::HLine);
     headerLine.setFrameShadow(QFrame::Sunken);
     headerLine.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Maximum);
 
     contentArea.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
 
     // start out collapsed
     contentArea.setMaximumHeight(0);
     contentArea.setMinimumHeight(0);
     contentArea.setVisible(false);
 
     // let the entire widget grow and shrink with its content
     toggleAnimation.addAnimation(new QPropertyAnimation(this, "minimumHeight"));
     toggleAnimation.addAnimation(new QPropertyAnimation(this, "maximumHeight"));
     toggleAnimation.addAnimation(new QPropertyAnimation(&contentArea, "maximumHeight"));
 
     mainLayout.setVerticalSpacing(0);
     mainLayout.setContentsMargins(0, 0, 0, 0);
     int row = 0;
     mainLayout.addWidget(&toggleButton, row, 0, 1, 1, Qt::AlignLeft);
     mainLayout.addWidget(&headerLine, row++, 2, 1, 1);
     mainLayout.addWidget(&contentArea, row, 0, 1, 3);
     setLayout(&mainLayout);
     QObject::connect(&toggleButton, &QToolButton::clicked, [this](const bool checked) {
         if (checked) {
             // make the content visible when expanding starts
             contentArea.setVisible(true);
         }
         toggleButton.setArrowType(checked ? Qt::ArrowType::DownArrow : Qt::ArrowType::RightArrow);
         toggleAnimation.setDirection(checked ? QAbstractAnimation::Forward : QAbstractAnimation::Backward);
         toggleAnimation.start();
     });
     connect(&toggleAnimation, &QAbstractAnimation::finished, [this]() {
         // hide the content area when it is fully collapsed
         if (!toggleButton.isChecked()) {
             contentArea.setVisible(false);
         }
     });
 }
 
 void AnimatedExpander::setContentLayout(QLayout *contentLayout)
 {
     delete contentArea.layout();
     contentArea.setLayout(contentLayout);
     const auto collapsedHeight = sizeHint().height() - contentArea.maximumHeight();
     auto contentHeight = contentLayout->sizeHint().height();
     for (int i = 0; i < toggleAnimation.animationCount() - 1; ++i) {
         auto expanderAnimation = static_cast<QPropertyAnimation *>(toggleAnimation.animationAt(i));
         expanderAnimation->setDuration(animationDuration);
         expanderAnimation->setStartValue(collapsedHeight);
         expanderAnimation->setEndValue(collapsedHeight + contentHeight);
     }
     auto contentAnimation = static_cast<QPropertyAnimation *>(toggleAnimation.animationAt(toggleAnimation.animationCount() - 1));
     contentAnimation->setDuration(animationDuration);
     contentAnimation->setStartValue(0);
     contentAnimation->setEndValue(contentHeight);
 }
 
 class SecKeyFilter : public DefaultKeyFilter
 {
 public:
     SecKeyFilter()
         : DefaultKeyFilter()
     {
         setRevoked(DefaultKeyFilter::NotSet);
         setExpired(DefaultKeyFilter::NotSet);
         setHasSecret(DefaultKeyFilter::Set);
         setCanCertify(DefaultKeyFilter::Set);
         setIsOpenPGP(DefaultKeyFilter::Set);
     }
 
     bool matches(const GpgME::Key &key, Kleo::KeyFilter::MatchContexts contexts) const override
     {
         if (!(availableMatchContexts() & contexts)) {
             return false;
         }
         if (_detail::ByFingerprint<std::equal_to>()(key, mExcludedKey)) {
             return false;
         }
         return DefaultKeyFilter::matches(key, contexts);
     }
 
     void setExcludedKey(const GpgME::Key &key)
     {
         mExcludedKey = key;
     }
 
 private:
     GpgME::Key mExcludedKey;
 };
 
-class UserIDItem : public QStandardItem
-{
-public:
-    explicit UserIDItem(const GpgME::UserID &uid)
-        : mUserId{uid}
-    {
-    }
-
-    GpgME::UserID userId()
-    {
-        return mUserId;
-    }
-
-private:
-    GpgME::UserID mUserId;
-};
-
-class UserIDModel : public QStandardItemModel
-{
-    Q_OBJECT
-public:
-    enum Role { UserID = Qt::UserRole };
-    explicit UserIDModel(QObject *parent = nullptr)
-        : QStandardItemModel(parent)
-    {
-    }
-
-    GpgME::Key certificateToCertify() const
-    {
-        return m_key;
-    }
-
-    void setKey(const GpgME::Key &key)
-    {
-        m_key = key;
-        clear();
-        const std::vector<GpgME::UserID> ids = key.userIDs();
-        int i = 0;
-        for (const auto &uid : key.userIDs()) {
-            if (uid.isRevoked() || uid.isInvalid() || Kleo::isRevokedOrExpired(uid)) {
-                // Skip user IDs that cannot really be certified.
-                i++;
-                continue;
-            }
-            const auto item = new UserIDItem{uid};
-            item->setText(Formatting::prettyUserID(uid));
-            item->setCheckable(true);
-            item->setEditable(false);
-            item->setCheckState(Qt::Checked);
-            appendRow(item);
-            i++;
-        }
-    }
-
-    void setCheckedUserIDs(const std::vector<GpgME::UserID> &uids)
-    {
-        for (int i = 0, end = rowCount(); i != end; ++i) {
-            const auto uidItem = userIdItem(i);
-            const auto itemUserId = uidItem->userId();
-            const bool userIdIsInList = Kleo::any_of(uids, [itemUserId](const auto &uid) {
-                return Kleo::userIDsAreEqual(itemUserId, uid);
-            });
-            uidItem->setCheckState(userIdIsInList ? Qt::Checked : Qt::Unchecked);
-        }
-    }
-
-    std::vector<GpgME::UserID> checkedUserIDs() const
-    {
-        std::vector<GpgME::UserID> userIds;
-        userIds.reserve(rowCount());
-        for (int i = 0; i < rowCount(); ++i) {
-            const auto uidItem = userIdItem(i);
-            if (uidItem->checkState() == Qt::Checked) {
-                userIds.push_back(uidItem->userId());
-            }
-        }
-        qCDebug(KLEOPATRA_LOG) << "Checked user IDs:" << userIds;
-        return userIds;
-    }
-
-private:
-    UserIDItem *userIdItem(int row) const
-    {
-        return static_cast<UserIDItem *>(item(row));
-    }
-
-private:
-    GpgME::Key m_key;
-};
-
 auto checkBoxSize(const QCheckBox *checkBox)
 {
     QStyleOptionButton opt;
     return checkBox->style()->sizeFromContents(QStyle::CT_CheckBox, &opt, QSize(), checkBox);
 }
 
-class ListView : public QListView
+class TreeWidget : public NavigatableTreeWidget
 {
     Q_OBJECT
 public:
-    using QListView::QListView;
+    using NavigatableTreeWidget::NavigatableTreeWidget;
 
 protected:
     void focusInEvent(QFocusEvent *event) override
     {
-        QListView::focusInEvent(event);
+        NavigatableTreeWidget::focusInEvent(event);
         // queue the invokation, so that it happens after the widget itself got focus
-        QMetaObject::invokeMethod(this, &ListView::forceAccessibleFocusEventForCurrentItem, Qt::QueuedConnection);
+        QMetaObject::invokeMethod(this, &TreeWidget::forceAccessibleFocusEventForCurrentItem, Qt::QueuedConnection);
     }
 
 private:
     void forceAccessibleFocusEventForCurrentItem()
     {
         // force Qt to send a focus event for the current item to accessibility
         // tools; otherwise, the user has no idea which item is selected when the
         // list gets keyboard input focus
         const auto current = currentIndex();
         setCurrentIndex({});
         setCurrentIndex(current);
     }
 };
-
 }
 
 class CertifyWidget::Private
 {
+    enum Role { UserIdRole = Qt::UserRole };
+
 public:
     Private(CertifyWidget *qq)
         : q{qq}
     {
         auto mainLay = new QVBoxLayout{q};
 
         {
             auto label = new QLabel{i18n("Verify the fingerprint, mark the user IDs you want to certify, "
                                          "and select the key you want to certify the user IDs with.<br>"
                                          "<i>Note: Only the fingerprint clearly identifies the key and its owner.</i>"),
                                     q};
             label->setWordWrap(true);
             labelHelper.addLabel(label);
             mainLay->addWidget(label);
         }
 
         mainLay->addWidget(new KSeparator{Qt::Horizontal, q});
 
         {
             auto grid = new QGridLayout;
             grid->setColumnStretch(1, 1);
             int row = -1;
 
             row++;
             mFprField = std::make_unique<InfoField>(i18n("Fingerprint:"), q);
             grid->addWidget(mFprField->label(), row, 0);
             grid->addLayout(mFprField->layout(), row, 1);
 
             row++;
             auto label = new QLabel{i18n("Certify with:"), q};
             mSecKeySelect = new KeySelectionCombo{/* secretOnly= */ true, q};
             mSecKeySelect->setKeyFilter(std::make_shared<SecKeyFilter>());
             label->setBuddy(mSecKeySelect);
             grid->addWidget(label, row, 0);
             grid->addWidget(mSecKeySelect);
 
             mainLay->addLayout(grid);
         }
 
         mMissingOwnerTrustInfo = new KMessageWidget{q};
         mSetOwnerTrustAction = new QAction{q};
         mSetOwnerTrustAction->setText(i18nc("@action:button", "Set Owner Trust"));
         mSetOwnerTrustAction->setToolTip(i18nc("@info:tooltip",
                                                "Click to set the trust level of the selected certification key to ultimate trust. "
                                                "This is what you usually want to do for your own keys."));
         connect(mSetOwnerTrustAction, &QAction::triggered, q, [this]() {
             setOwnerTrust();
         });
         mMissingOwnerTrustInfo->addAction(mSetOwnerTrustAction);
         mMissingOwnerTrustInfo->setVisible(false);
 
         mainLay->addWidget(mMissingOwnerTrustInfo);
 
         mainLay->addWidget(new KSeparator{Qt::Horizontal, q});
 
-        userIdListView = new ListView{q};
+        userIdListView = new TreeWidget{q};
         userIdListView->setAccessibleName(i18n("User IDs"));
-        userIdListView->setModel(&mUserIDModel);
+        userIdListView->setEditTriggers(QAbstractItemView::NoEditTriggers);
+        userIdListView->setSelectionMode(QAbstractItemView::SingleSelection);
+        userIdListView->setRootIsDecorated(false);
+        userIdListView->setUniformRowHeights(true);
+        userIdListView->setAllColumnsShowFocus(false);
+        userIdListView->setHeaderHidden(true);
+        userIdListView->setHeaderLabels({i18nc("@title:column", "User ID")});
         mainLay->addWidget(userIdListView, 1);
 
         // Setup the advanced area
         auto expander = new AnimatedExpander{i18n("Advanced"), i18n("Show advanced options"), q};
         mainLay->addWidget(expander);
 
         auto advLay = new QVBoxLayout;
 
         mExportCB = new QCheckBox{q};
         mExportCB->setText(i18n("Certify for everyone to see (exportable)"));
         advLay->addWidget(mExportCB);
 
         {
             auto layout = new QHBoxLayout;
 
             mPublishCB = new QCheckBox{q};
             mPublishCB->setText(i18n("Publish on keyserver afterwards"));
             mPublishCB->setEnabled(mExportCB->isChecked());
 
             layout->addSpacing(checkBoxSize(mExportCB).width());
             layout->addWidget(mPublishCB);
 
             advLay->addLayout(layout);
         }
 
         {
             auto tagsLay = new QHBoxLayout;
 
             auto label = new QLabel{i18n("Tags:"), q};
             mTagsLE = new QLineEdit{q};
             label->setBuddy(mTagsLE);
 
             const auto tooltip = i18n("You can use this to add additional info to a certification.") + QStringLiteral("<br/><br/>")
                 + i18n("Tags created by anyone with full certification trust "
                        "are shown in the keylist and can be searched.");
             label->setToolTip(tooltip);
             mTagsLE->setToolTip(tooltip);
 
             tagsLay->addWidget(label);
             tagsLay->addWidget(mTagsLE, 1);
 
             advLay->addLayout(tagsLay);
         }
 
         {
             auto layout = new QHBoxLayout;
 
             mExpirationCheckBox = new QCheckBox{q};
             mExpirationCheckBox->setText(i18n("Expiration:"));
 
             mExpirationDateEdit = new KDateComboBox{q};
             Kleo::setUpExpirationDateComboBox(mExpirationDateEdit, {QDate::currentDate().addDays(1), QDate{}});
             mExpirationDateEdit->setDate(Kleo::defaultExpirationDate(ExpirationOnUnlimitedValidity::InternalDefaultExpiration));
             mExpirationDateEdit->setEnabled(mExpirationCheckBox->isChecked());
 
             const auto tooltip = i18n("You can use this to set an expiration date for a certification.") + QStringLiteral("<br/><br/>")
                 + i18n("By setting an expiration date, you can limit the validity of "
                        "your certification to a certain amount of time. Once the expiration "
                        "date has passed, your certification is no longer valid.");
             mExpirationCheckBox->setToolTip(tooltip);
             mExpirationDateEdit->setToolTip(tooltip);
 
             layout->addWidget(mExpirationCheckBox);
             layout->addWidget(mExpirationDateEdit, 1);
 
             advLay->addLayout(layout);
         }
 
         {
             mTrustSignatureCB = new QCheckBox{q};
             mTrustSignatureCB->setText(i18n("Certify as trusted introducer"));
             const auto tooltip = i18n("You can use this to certify a trusted introducer for a domain.") + QStringLiteral("<br/><br/>")
                 + i18n("All certificates with email addresses belonging to the domain "
                        "that have been certified by the trusted introducer are treated "
                        "as certified, i.e. a trusted introducer acts as a kind of "
                        "intermediate CA for a domain.");
             mTrustSignatureCB->setToolTip(tooltip);
 
             advLay->addWidget(mTrustSignatureCB);
         }
         {
             auto layout = new QHBoxLayout;
 
             auto label = new QLabel{i18n("Domain:"), q};
 
             mTrustSignatureDomainLE = new QLineEdit{q};
             mTrustSignatureDomainLE->setEnabled(mTrustSignatureCB->isChecked());
             label->setBuddy(mTrustSignatureDomainLE);
 
             layout->addSpacing(checkBoxSize(mTrustSignatureCB).width());
             layout->addWidget(label);
             layout->addWidget(mTrustSignatureDomainLE);
 
             advLay->addLayout(layout);
         }
 
         expander->setContentLayout(advLay);
 
-        connect(&mUserIDModel, &QStandardItemModel::itemChanged, q, [this](QStandardItem *item) {
+        connect(userIdListView, &QTreeWidget::itemChanged, q, [this](auto item, auto) {
             onItemChanged(item);
         });
 
         connect(mExportCB, &QCheckBox::toggled, [this](bool on) {
             mPublishCB->setEnabled(on);
         });
 
         connect(mSecKeySelect, &KeySelectionCombo::currentKeyChanged, [this](const GpgME::Key &) {
             updateTags();
             checkOwnerTrust();
             Q_EMIT q->changed();
         });
 
         connect(mExpirationCheckBox, &QCheckBox::toggled, q, [this](bool checked) {
             mExpirationDateEdit->setEnabled(checked);
             Q_EMIT q->changed();
         });
         connect(mExpirationDateEdit, &KDateComboBox::dateChanged, q, &CertifyWidget::changed);
 
         connect(mTrustSignatureCB, &QCheckBox::toggled, q, [this](bool on) {
             mTrustSignatureDomainLE->setEnabled(on);
             Q_EMIT q->changed();
         });
         connect(mTrustSignatureDomainLE, &QLineEdit::textChanged, q, &CertifyWidget::changed);
 
         loadConfig();
     }
 
     ~Private() = default;
 
     void loadConfig()
     {
         const Settings settings;
         mExpirationCheckBox->setChecked(settings.certificationValidityInDays() > 0);
         if (settings.certificationValidityInDays() > 0) {
             const QDate expirationDate = QDate::currentDate().addDays(settings.certificationValidityInDays());
             mExpirationDateEdit->setDate(expirationDate > mExpirationDateEdit->maximumDate() //
                                              ? mExpirationDateEdit->maximumDate() //
                                              : expirationDate);
         }
 
         const KConfigGroup conf(KSharedConfig::openConfig(), "CertifySettings");
         mSecKeySelect->setDefaultKey(conf.readEntry("LastKey", QString()));
         mExportCB->setChecked(conf.readEntry("ExportCheckState", false));
         mPublishCB->setChecked(conf.readEntry("PublishCheckState", false));
     }
 
+    void setUpUserIdList()
+    {
+        userIdListView->clear();
+        for (const auto &uid : mTarget.userIDs()) {
+            if (uid.isInvalid() || Kleo::isRevokedOrExpired(uid)) {
+                // Skip user IDs that cannot really be certified.
+                continue;
+            }
+            auto item = new QTreeWidgetItem;
+            item->setData(0, UserIdRole, QVariant::fromValue(uid));
+            item->setData(0, Qt::DisplayRole, Kleo::Formatting::prettyUserID(uid));
+            item->setFlags(Qt::ItemIsSelectable | Qt::ItemIsUserCheckable | Qt::ItemIsEnabled);
+            item->setCheckState(0, Qt::Checked);
+            userIdListView->addTopLevelItem(item);
+        }
+    }
+
     void updateTags()
     {
         if (mTagsLE->isModified()) {
             return;
         }
         GpgME::Key remarkKey = mSecKeySelect->currentKey();
 
         if (!remarkKey.isNull()) {
             std::vector<GpgME::UserID> uidsWithRemark;
             QString remark;
             for (const auto &uid : mTarget.userIDs()) {
                 GpgME::Error err;
                 const char *c_remark = uid.remark(remarkKey, err);
                 if (c_remark) {
                     const QString candidate = QString::fromUtf8(c_remark);
                     if (candidate != remark) {
                         qCDebug(KLEOPATRA_LOG) << "Different remarks on user IDs. Taking last.";
                         remark = candidate;
                         uidsWithRemark.clear();
                     }
                     uidsWithRemark.push_back(uid);
                 }
             }
             // Only select the user IDs with the correct remark
             if (!remark.isEmpty()) {
                 selectUserIDs(uidsWithRemark);
             }
             mTagsLE->setText(remark);
         }
     }
 
     void updateTrustSignatureDomain()
     {
         if (mTrustSignatureDomainLE->text().isEmpty() && mTarget.numUserIDs() == 1) {
             // try to guess the domain to use for the trust signature
             const auto address = mTarget.userID(0).addrSpec();
             const auto atPos = address.find('@');
             if (atPos != std::string::npos) {
                 const auto domain = address.substr(atPos + 1);
                 mTrustSignatureDomainLE->setText(QString::fromUtf8(domain.c_str(), domain.size()));
             }
         }
     }
 
     void setTarget(const GpgME::Key &key)
     {
         mFprField->setValue(QStringLiteral("<b>") + Formatting::prettyID(key.primaryFingerprint()) + QStringLiteral("</b>"),
                             Formatting::accessibleHexID(key.primaryFingerprint()));
-        mUserIDModel.setKey(key);
         mTarget = key;
+        setUpUserIdList();
 
         auto keyFilter = std::make_shared<SecKeyFilter>();
         keyFilter->setExcludedKey(mTarget);
         mSecKeySelect->setKeyFilter(keyFilter);
 
         updateTags();
         updateTrustSignatureDomain();
     }
 
     GpgME::Key secKey() const
     {
         return mSecKeySelect->currentKey();
     }
 
+    GpgME::UserID getUserId(const QTreeWidgetItem *item) const
+    {
+        return item ? item->data(0, UserIdRole).value<UserID>() : UserID{};
+    }
+
     void selectUserIDs(const std::vector<GpgME::UserID> &uids)
     {
-        mUserIDModel.setCheckedUserIDs(uids);
+        for (int i = 0, end = userIdListView->topLevelItemCount(); i < end; ++i) {
+            const auto uidItem = userIdListView->topLevelItem(i);
+            const auto itemUserId = getUserId(uidItem);
+            const bool userIdIsInList = Kleo::any_of(uids, [itemUserId](const auto &uid) {
+                return Kleo::userIDsAreEqual(itemUserId, uid);
+            });
+            uidItem->setCheckState(0, userIdIsInList ? Qt::Checked : Qt::Unchecked);
+        }
     }
 
     std::vector<GpgME::UserID> selectedUserIDs() const
     {
-        return mUserIDModel.checkedUserIDs();
+        std::vector<GpgME::UserID> userIds;
+        userIds.reserve(userIdListView->topLevelItemCount());
+        for (int i = 0, end = userIdListView->topLevelItemCount(); i < end; ++i) {
+            const auto *const uidItem = userIdListView->topLevelItem(i);
+            if (uidItem->checkState(0) == Qt::Checked) {
+                userIds.push_back(getUserId(uidItem));
+            }
+        }
+        qCDebug(KLEOPATRA_LOG) << "Checked user IDs:" << userIds;
+        return userIds;
     }
 
     bool exportableSelected() const
     {
         return mExportCB->isChecked();
     }
 
     bool publishSelected() const
     {
         return mPublishCB->isChecked();
     }
 
     QString tags() const
     {
         return mTagsLE->text().trimmed();
     }
 
     GpgME::Key target() const
     {
         return mTarget;
     }
 
     bool isValid() const
     {
         static const QRegularExpression domainNameRegExp{QStringLiteral(R"(^\s*((xn--)?[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}\s*$)"),
                                                          QRegularExpression::CaseInsensitiveOption};
 
         // do not accept null keys
         if (mTarget.isNull() || mSecKeySelect->currentKey().isNull()) {
             return false;
         }
         // do not accept empty list of user IDs
         if (selectedUserIDs().empty()) {
             return false;
         }
         // do not accept if the key to certify is selected as certification key;
         // this shouldn't happen because the key to certify is excluded from the choice, but better safe than sorry
         if (_detail::ByFingerprint<std::equal_to>()(mTarget, mSecKeySelect->currentKey())) {
             return false;
         }
         if (mExpirationCheckBox->isChecked() && !mExpirationDateEdit->isValid()) {
             return false;
         }
         if (mTrustSignatureCB->isChecked() && !domainNameRegExp.match(mTrustSignatureDomainLE->text()).hasMatch()) {
             return false;
         }
         return true;
     }
 
     void checkOwnerTrust()
     {
         const auto secretKey = secKey();
         if (secretKey.ownerTrust() != GpgME::Key::Ultimate) {
             mMissingOwnerTrustInfo->setMessageType(KMessageWidget::Information);
             mMissingOwnerTrustInfo->setIcon(QIcon::fromTheme(QStringLiteral("question")));
             mMissingOwnerTrustInfo->setText(i18n("Is this your own key?"));
             mSetOwnerTrustAction->setEnabled(true);
             mMissingOwnerTrustInfo->animatedShow();
         } else {
             mMissingOwnerTrustInfo->animatedHide();
         }
     }
 
     void setOwnerTrust()
     {
         mSetOwnerTrustAction->setEnabled(false);
         QGpgME::ChangeOwnerTrustJob *const j = QGpgME::openpgp()->changeOwnerTrustJob();
         connect(j, &QGpgME::ChangeOwnerTrustJob::result, q, [this](const GpgME::Error &err) {
             if (err) {
                 KMessageBox::error(q,
                                    i18n("<p>Changing the certification trust of the key <b>%1</b> failed:</p><p>%2</p>",
                                         Formatting::formatForComboBox(secKey()),
                                         Formatting::errorAsString(err)),
                                    i18n("Certification Trust Change Failed"));
             }
             if (err || err.isCanceled()) {
                 mSetOwnerTrustAction->setEnabled(true);
             } else {
                 mMissingOwnerTrustInfo->setMessageType(KMessageWidget::Positive);
                 mMissingOwnerTrustInfo->setIcon(QIcon::fromTheme(QStringLiteral("checkmark")));
                 mMissingOwnerTrustInfo->setText(i18n("Owner trust set successfully."));
             }
         });
         j->start(secKey(), GpgME::Key::Ultimate);
     }
 
-    void onItemChanged(QStandardItem *item)
+    void onItemChanged(QTreeWidgetItem *item)
     {
         Q_EMIT q->changed();
 
 #ifndef QT_NO_ACCESSIBILITY
         if (item) {
             // assume that the checked state changed
             QAccessible::State st;
             st.checked = true;
             QAccessibleStateChangeEvent e(userIdListView, st);
-            e.setChild(item->index().row());
+            e.setChild(userIdListView->indexOfTopLevelItem(item));
             QAccessible::updateAccessibility(&e);
         }
 #endif
     }
 
 public:
     CertifyWidget *const q;
     std::unique_ptr<InfoField> mFprField;
     KeySelectionCombo *mSecKeySelect = nullptr;
     KMessageWidget *mMissingOwnerTrustInfo = nullptr;
-    ListView *userIdListView = nullptr;
+    NavigatableTreeWidget *userIdListView = nullptr;
     QCheckBox *mExportCB = nullptr;
     QCheckBox *mPublishCB = nullptr;
     QLineEdit *mTagsLE = nullptr;
     QCheckBox *mTrustSignatureCB = nullptr;
     QLineEdit *mTrustSignatureDomainLE = nullptr;
     QCheckBox *mExpirationCheckBox = nullptr;
     KDateComboBox *mExpirationDateEdit = nullptr;
     QAction *mSetOwnerTrustAction = nullptr;
 
     LabelHelper labelHelper;
 
-    UserIDModel mUserIDModel;
     GpgME::Key mTarget;
 };
 
 CertifyWidget::CertifyWidget(QWidget *parent)
     : QWidget{parent}
     , d{std::make_unique<Private>(this)}
 {
 }
 
 Kleo::CertifyWidget::~CertifyWidget() = default;
 
 void CertifyWidget::setTarget(const GpgME::Key &key)
 {
     d->setTarget(key);
 }
 
 GpgME::Key CertifyWidget::target() const
 {
     return d->target();
 }
 
 void CertifyWidget::selectUserIDs(const std::vector<GpgME::UserID> &uids)
 {
     d->selectUserIDs(uids);
 }
 
 std::vector<GpgME::UserID> CertifyWidget::selectedUserIDs() const
 {
     return d->selectedUserIDs();
 }
 
 GpgME::Key CertifyWidget::secKey() const
 {
     return d->secKey();
 }
 
 bool CertifyWidget::exportableSelected() const
 {
     return d->exportableSelected();
 }
 
 QString CertifyWidget::tags() const
 {
     return d->tags();
 }
 
 bool CertifyWidget::publishSelected() const
 {
     return d->publishSelected();
 }
 
 bool CertifyWidget::trustSignatureSelected() const
 {
     return d->mTrustSignatureCB->isChecked();
 }
 
 QString CertifyWidget::trustSignatureDomain() const
 {
     return d->mTrustSignatureDomainLE->text().trimmed();
 }
 
 QDate CertifyWidget::expirationDate() const
 {
     return d->mExpirationCheckBox->isChecked() ? d->mExpirationDateEdit->date() : QDate{};
 }
 
 bool CertifyWidget::isValid() const
 {
     return d->isValid();
 }
 
 // For UserID model
 #include "certifywidget.moc"