title: How come changes to tree structure don't propogate between multiple NSOutlineViews/NSTreeControllers using cocoa bindings?
body: <p>In my project I have two NSOutlineViews set up as below:</p>
  
  <p><img src="https://i.stack.imgur.com/TBf0j.png" alt="enter image description here"></p>
  
  <p>The right side is the sub-tree of the selection in the left side and is set up using cocoa bindings using two NSTreeControllers, where the right side is binded to the selection property of the left side. If I add a sub item to the right side as is shown below, the same item in the left side does not become expandable.</p>
  
  <p>I've looked all over for an answer to this, but the only solution I can find so far is to manually call display on the view. Any ideas?</p>