title: How to get all children of queryset in django?
body: <p>I've a queryset result, say, animals, which has a list of animals. There are sub categories of animals and I want to get all the subcategories. i.e.</p>
  
  <p>for single animal, I can use <code>animal.categories</code> which works. Now, I want to somehow do this:</p>
  
  <pre><code>categories = animals.categories
  </code></pre>
  
  <p>where animals is queryset. How can I achieve this?</p>