Treeview inside Window editor is not scrolling.

As you can see in the image attatched. The treeview does not scroll even though it is a huge list of items. Things I have tried so far

 float startY = controlRect.y + controlRect.height + 12;
             Rect r = new Rect(0, startY, position.width, position.height - startY);
 
 
             m_TreeViewState.scrollPos = EditorGUILayout.BeginScrollView(m_TreeViewState.scrollPos, true ,true,
                 GUILayout.Width(r.width) , GUILayout.Height(r.height));
 
             
             m_SimpleTreeView.OnGUI(r);
 
             
             EditorGUILayout.EndScrollView();
             
             EditorGUILayout.EndVertical();

I have also tried toggling useScrollView. all to no effect. Can someone tell me what I am doing wrong? thank you very much.