TreeView assertion failure on appending items into expanded, non-empty, non-root parent

Reproduce:

• Configure, build and run the project TreeViewTest in the attachment.
• Expand the root item at top.
• Click "Append" twice, and the assertion failure will occur on the second click.

As the title says, the assertion failure happens ONLY when appending items (not prepending or inserting in the middle), non-empty parent (so the first click runs fine), non-root parent (the parent passed into ListModel::beginInsertRows is not QModelIndex()), and the corresponding node is expanded in TreeView.

Don't know if this is the side effect of QTBUG-66062.