code: def get_node(self, index):
          
  
          if not index.isValid():
              return self.__root_node
          return index.internalPointer() or self.__root_node
docs: Returns the Node at given index.
  
          :param index: Index.
          :type index: QModelIndex
          :return: Node.
          :rtype: AbstractCompositeNode or GraphModelNode