code: def leaves(self):
          
          # We need to read the _cte_node_children attribute, so ensure it exists.
          self._ensure_parameters()
          return self.exclude(
              **{"%s__id__in" % self.model._cte_node_children: self.all()}
          )
docs: Returns a :class:`QuerySet` of all leaf nodes (nodes with no
              children).
  
              :return: A :class:`QuerySet` of all leaf nodes (nodes with no
                  children).