docs: def setItemStyle(self, itemStyle):
          """
          Sets the item style that will be used for this widget.  If you are
          trying to set a style on an item that has children, make sure to turn 
          off the useGroupStyleWithChildren option, or it will always display as
          a group.
          
          :param      itemStyle | <XGanttWidgetItem.ItemStyle>
          """
          self._itemStyle = itemStyle
          
          # initialize the group icon for group style
          if itemStyle == XGanttWidgetItem.ItemStyle.Group and \
             self.icon(0).isNull():
              ico = projexui.resources.find('img/folder_close.png')
              expand_ico = projexui.resources.find('img/folder_open.png')
              self.setIcon(0, QIcon(ico))
              self.setExpandedIcon(0, QIcon(expand_ico))