It turns out the Win32 tree view control has a novel way of selecting items. If you hold down Shift and scroll your mouse wheel up (but not down!) it will select the item underneath the pointer.
This even works in the Windows 10 File Explorer. Hover over the text of an item in the left-hand pane (so the hand pointer appears), hold Shift and scroll the mouse wheel up. The folder will be opened.
There may be some method to this madness. If you instead hover over the expand or collapse icon for an item, scrolling the mouse wheel down will collapse the item, and scrolling the mouse wheel up will expand it (which is backwards if you ask me, but never mind).
The behaviour is present in Windows 7 (as long as the tree view is focused or otherwise receiving mouse wheel messages), so it’s been there for a while. (Of course, none of this works on the new Windows App SDK-based File Explorer rolling out for Windows 11, but it still works in the Registry Editor there.)