Deleting lots of QTreeWidgetItems is extremely slow

Removing a large number of items from a QTreeWidget seems to be extremely slow. In a tree with three levels and about 100,000 leaf nodes, removing a large number of the leaf items in one go takes several minutes. Nothing I tried makes a difference: turning off updates with setUpdatesEnabled(false), sorting the items in reverse order of their place in the tree before carrying out the removal, removeChild instead of just deleting each QTreeWidgetItem, takeChild instead of removeChild... nothing seems to work.