WPF MVVM TreeView IsSelected绑定无法正常工作

I have a problem that I cannot see why it's not working. I have a 3 level Treeview with a converter which allow me to invert the two first level. On this TreeView I'm trying to bing the IsSelected Property but for a reason I don't understand it is never call in the ViewModel. I have a problem that I cannot see why it's not