title: Fast get all subusers of specific node in django users table
body: <p>I have django model:</p>
  
  <pre><code>class Profile(models.Model): 
      user = models.OneToOneField(User)
      parent = models.ForeignKey(User, related_name='parent_user_for_profile')
  </code></pre>
  
  <p>How to create function which returns all the child users.</p>
  
  <p>For example <a href="https://i.stack.imgur.com/na1vf.jpg" rel="nofollow noreferrer">See picture of hierarchy</a></p>
  
  <pre><code>For n12 - [n122, n1211б n121, dsf]
  For n1 - [n12, n11, n122, n1211, n121, dsf]
  For n2 - [n21, n212]
  </code></pre>