Focus on QTreeWidgetItem

I'm using a QTreeWidget, with root, parents, children, and grandchildren. How do I remove the focus from the QTreeWidgetItems representing the parents and children so that the arrow keys step through the grandchildren?

I have set the flags to Qt::ItemIsEnabled, but not set Qt::ItemIsSelectable, for the parents and children. Mouse clicks and the arrows still set focus on the parents and children. Most likely, I missed something.

Thanks for any help.