During your typing Program Tree Editor updates the tree automatically.
How often it depends on value of option: Rebuld Tree When.

If value is immediately, then the tree is updated after any key press.
If value is string lost focus , Program Tree Editor waits when you finish type a string.
If value is node lost focus , editor updates the tree after leaving a node.

Default value is string lost focus .

Also, you can press F8 and the tree will updated immediately.