Sets whether or not to use arrows for the grouping mechanism.
        
        :param      state | <bool>

def setArrowStyle( self, state ):
        """
        Sets whether or not to use arrows for the grouping mechanism.
        
        :param      state | <bool>
        """
        self._arrowStyle = state
        
        if not state:
            self.setStyleSheet('')
        else:
            right = resources.find('img/treeview/triangle_right.png')
            down  = resources.find('img/treeview/triangle_down.png')
            opts  = (right.replace('\\', '/'), down.replace('\\', '/'))
            self.setStyleSheet(ARROW_STYLESHEET % opts)