How to hide / show a TreeNode

I have a TreeGrid upon which I set a Tree which has TreeNodes.

OK, shows fine.

Now, I want to programmatically show or hide some of the leaf TreeNodes on the TreeGrid based upon user interaction with other parts of the GUI.

How can I show or hide a TreeNode?

My TreeGrid is not DataSource bound. It is populated in code and always has the same nodes.
I just want to show some in one case and show others in another case.