code: def rowCount(self, parent):
          
          if parent.column() > 0:
              return 0
          if not parent.isValid():
              parentItem = self._root
          else:
              parentItem = parent.internalPointer()
          return parentItem.child_count()
docs: Return the number of rows under the given parent.
          When the parent is valid return rowCount the number
          of children of parent.
  
          :param parent: the parent index
          :type parent: :class:`QtCore.QModelIndex`:
          :returns: the row count
          :rtype: int
          :raises: None