Hello Doug,
You can put the ItemContainerStyle either in the UserControl.Resources:
Or you can put it inline with RadTreeListView's definition:
However, it is strange that that you are experiencing this issue.
I am attaching the source code of
RadTreeListView's FirstLook example. It demonstrates the IsExpanded functionality. Have a look at it and if you have additonal questions or you find something to be unclear, let me know as soon as possible. I'd be more than happy to assist you.
Greetings,
Kiril Stanoev
the Telerik team