code: def siblings(self, node):
          
          # We need to read the _cte_node_parent* attributes, so ensure they
          # exist.
          self._ensure_parameters()
          # We need to construct: filter(parent = node.parent_id)
          return self.filter(
              **{
                  self.model._cte_node_parent: getattr(
                      node, self.model._cte_node_parent_attname
                  )
              }
          ).exclude(id=node.id)
docs: Returns a :class:`QuerySet` of all siblings of a given
              :class:`CTENode` `node`.
  
              :param node: a :class:`CTENode` whose siblings are required.
  
              :returns: A :class:`QuerySet` of all siblings of the given `node`.