Here is a very quick example:

#DEFINE tvwFirst 0
#DEFINE tvwLast 1
#DEFINE tvwNext 2
#DEFINE tvwPrevious 3
#DEFINE tvwChild 4

THISFORM.TreeView.Nodes.Add(,tvwFirst,"Root","This is the Root Node" )
THISFORM.TreeView.Nodes.Add("Root", tvwChild, "Node1Parent", "This is Node 1 Parent" )
THISFORM.TreeView.Nodes.Add("Node1Parent", tvwChild, "Node1Child", "This is Node 1 Child" )
THISFORM.TreeView.Nodes.Add("Root", tvwChild, "Node2", "This is Node 2 Parent" )

If you are interested in adding images to the nodes, let me know and I will send you another quick sample. In the meantime, this should give you an idea as to how to populate the treeview.

Good luck!