Qt: Attempt to add Drag and Drop to Editable Tree Model example not working

I'm trying to learn how to implement Drag and Drop to model/view settings in Qt. As an exercise, I attempted to do that to the Editable Tree Model example available at the Qt web site:

To extend it with Drag and Drop, I followed the instructions in Qt's documentation on "Using Drag and Drop with View Items", more specifically "Using model/view classes".

I placed the code for my attempt at a GitHub repository. The main modifications are below but there are other important ones; here are the full changes according to the documentation.

/* mainwindow.cpp -- THIS IS NOT ALL CHANGES -- See link above for all changes */
view->setSelectionMode(QAbstractItemView::SingleSelection);
view->setDragEnabled(true);
view->viewport()->setAcceptDrops(true);
view->setDropIndicatorShown(true);
view->setDragDropMode(QAbstractItemView::DragDrop);

However, this didn't quite work. While I can drag and drop items, the copied item appears as blank. This can be seen in this screen capture, but the main screenshots are:

Note that the documentation describes the need to re-implement QAbstractItemModel's dropMimeData for drag and drop functionality, which I did not. This is because, upon inspecting the source code for that class, I find that its default implementation should already work in copying items in drag and drop, since it uses the default application/x-qabstractitemmodeldatalist MIME format and uses setItemData for the inserted items.

What is wrong here? Is it the default dropMimeData that's not working, or something else?

The model provided by the example only accepts setting data with role Qt::EditRole. See line 263 in treemodel.cpp

bool TreeModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    if (role != Qt::EditRole)
        return false;

    ...
}

Removing that part or adding Qt::DisplayRole and the data will be set properly.