title: Extract children with a given condition - Django MPTT and Django rest framework
body: <p><a href="https://i.stack.imgur.com/Xzjmk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Xzjmk.png" alt="enter image description here" /></a></p>
  <p>In this tree I want to do a query so that <strong>only</strong> the first generation of the red circle is extracted.
  But the condition is that the value of each circle must be greater than zero, ie the green circles:</p>
  <p><a href="https://i.stack.imgur.com/1vtlV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1vtlV.png" alt="enter image description here" /></a></p>
  <p>Serializers:</p>
  <pre><code>class CircleBaseSerializer(serializers.ModelSerializer):
      class Meta:
          model = Circle
          fields = ('id', 'value')
  
  
  class CircleChildrenSerializer(CircleBaseSerializer):
      class Meta(CircleBaseSerializer.Meta):
          pass
  
  class CircleParentSerializer(CircleBaseSerializer):
      children = CircleChildrenSerializer(many=True)
      class Meta(CircleBaseSerializer.Meta):
         pass
  </code></pre>
  <p>View:</p>
  <pre><code>class CircleViewSet(ReadOnlyModelViewSet):
      serializer_class = CircleParentSerializer
      queryset = Circle.objects.all()
      def get_queryset(self):
          id = self.kwargs[&quot;id&quot;]
          u=Circle.objects.get(pk=id)
  </code></pre>
  <p>Certainly result is [5(1,0,3)] that is not desirable.
  How can I do this query?</p>