You must use an ImageList control, which is a separate control from the Treeview. You would add images to that control, then add the entire ImageList control to the Treeview. How you setup and use the INdex and Key properties of the ImageList control, in conjunction with the Tab nodes and how you build them, determines which image shows up on a specific Node.
It's been a while since I've worked with the Microsoft treeview control. I long ago stopped using it, and use a 3rd party control (from Mabry, who unfortuantely is no longer in business).