You can use HTML-Like formatting, but I would advise against it in this case.
Me.RadTreeView1.Nodes.Add("<html>Here is some really long text, <br>I'm going to try and make it wrap</html>")
The node renders up to two lines (one line break) but when selecting the node, only the first line text will show as highlighted and this would be very confusing for the user as to where one node text stops and the next one starts, and may cause confusion when only the first line is showing as selected.