See the attached example.

It creates a standard item model, subclassed to enable drag & drop (for moving items around).
A standard sort filter proxy model is then created, with this model as source, and the proxy model added to a tree view with enabled drag & drop.

As long as the tree view's header does not have section resize mode ResizeToContents everything works as expected. But if it has, dropping an item crashes in Qt, while calculating header sizes.