code: def setExpanded(self, state):
          
          if state == self._expanded:
              return
          
          self._expanded = state
          
          # update the button
          btn = self.widget()
          if btn:
              if state:
                  ico = 'img/treeview/triangle_down.png'
              else:
                  ico = 'img/treeview/triangle_right.png'
              btn.setIcon(QtGui.QIcon(resources.find(ico)))
          
          # update the children
          for child in self.children():
              child.setHidden(not state)
docs: Expands this group item to the inputed state.
          
          :param      state | <bool>