code: def headerData(self, section, orientation, role):
          
          if orientation == QtCore.Qt.Horizontal:
              d = self._root.data(section, role)
              if d is None and role == QtCore.Qt.DisplayRole:
                  return str(section+1)
              return d
          if orientation == QtCore.Qt.Vertical and role == QtCore.Qt.DisplayRole:
              return str(section+1)
docs: Return the header data
  
          Will call :meth:`TreeItem.data` of the root :class:`TreeItem` with the
          given section (column) and role for horizontal orientations.
  
          Vertical orientations are numbered.
  
          :param section: the section in the header view
          :type section: int
          :param orientation: vertical or horizontal orientation
          :type orientation: :data:`QtCore.Qt.Vertical` | :data:`QtCore.Qt.Horizontal`
          :param role: the data role.
          :type role: :data:`QtCore.Qt.ItemDataRole`
          :returns: data for the header
          :raises: None