Make QTreeView behave like nativ Mac tree view. When you have highligted an item in a tree view on Mac, pressing left will take yu to the parent item, and pressing left again will collapse the item (ref Finder). QTreeView should beehave the same way by default.

The only way of getting this now, is with SH_ItemView_ArrowKeysNavigateIntoChildren, which also gives you non native behavior of the right arrow key.