Windows Narrator reads out the position of the selected item within its current level when navigating a TreeView, for example, "3 of 8".

If the root item is hidden with a call to

setShowRoot(false);

Then there are now multiple items at the root level, and the first item at the root level will read out "1 of 1", but all other top level items will be read out as "0 of 1".

Run attached sample code as an example, and launch Windows Narrator and navigate the tree. If the root item is included then it all works as expected.