title: How do I rebuild my django-mptt tree?
body: <p>I'm using django-mptt 0.4.2, and want to rebuild a tree.</p>
  
  <p>The tree manager has a method rebuild() which I try to access like this:</p>
  
  <pre><code>&gt;&gt;&gt; my_rootnode = MyObj.objects.get(id=12)
  &gt;&gt;&gt; my_rootnode.tree.rebuild()
  Traceback (most recent call last):
    File "&lt;console&gt;", line 1, in &lt;module&gt;
    File "/usr/local/lib/python2.6/dist-packages/django/db/models/manager.py", line 211, in __get__
      raise AttributeError("Manager isn't accessible via %s instances" % type.__name__)
  AttributeError: Manager isn't accessible via MyObj instances
  </code></pre>
  
  <p>I'm obviously doing this wrong. How should I access the rebuild method?</p>