code: def related(self, collection_id):
          
          url = "/collections/%s/related" % collection_id
          result = self._get(url)
          return CollectionModel.parse_list(result)
docs: Retrieve a list of collections related to this one.
  
          :param collection_id [string]: The collection’s ID. Required.
          :return: [Array]: A single page of the Collection list.