I tried to reproduce your problem but to no avail - the RadTreeView
is rendered as expected and the [+] elements are visible and functional.
As to your other questions:
- Yes, you can define/add/remove nodes programmatically in the standard manner.
- RadToolTip and RadToolTipManager are different classes and you don't need to have both of them to show a tooltip.
I prepared a sample project which demonstrates the described by you scenario - you can find it in the attached archive.
the Telerik team