IsExpanded not function at init status

[chy001a]

examples:
in DemoTreeViewModel.cs
change var a = MyTree.Children.Add(new DemoTreeNode { Title = "Branch A", Score = 0.75, IsExpanded = true });
to var a = MyTree.Children.Add(new DemoTreeNode { Title = "Branch A", Score = 0.75, IsExpanded = false });

not effect!