code: def add_chunk(self,chunk_obj):
          
          if self.chunk_layer is None:
              self.chunk_layer = Cchunks(type=self.type)
              self.root.append(self.chunk_layer.get_node())
          self.chunk_layer.add_chunk(chunk_obj)
docs: Adds a chunk to the chunk layer
          @type chunk_obj: L{Cchunk}
          @param chunk_obj: the chunk object