title: Django - Models - Recursively retrieve parents of a leaf node
body: <p>I have a User model class defined as follows:</p>
  
  <pre><code>class CustomUser(models.Model):
      user = models.OneToOneField(User)
      slug = models.SlugField(max_length=35, unique=True,help_text="URI dell'utente che appare sul browser")
      team = models.CharField(max_length=100, null=False, verbose_name="Team")
      area = models.CharField(max_length=100, null=False, verbose_name="Area")
      line_manager = models.ForeignKey('self', null=True, blank=True,related_name='parent')
  </code></pre>
  
  <p><strong>I would like to retrieve all the line_managers of a CustomUser.</strong> 
  Let's suppose I have:</p>
  
  <pre><code>A
  -B 
   -C
  </code></pre>
  
  <p>where C is the leaf and B and A are the values I would like to retrieve.
  How can I do in django?</p>