Maybe you can override the dropEvent ( QDropEvent * event ) from QAbstractItemView in your QTreeView and do something like that

Qt Code:
  1. void MyTreeView::dropEvent(QDropEvent * event)
  2. {
  3. QModelIndex dropIndex = indexAt(event->pos());
  4. if (!dropIndex.parent().isValid()) { // if i have no parent, let the event do his job
  5. QTreeView::dropEvent(event);
  6. }
  7. }
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