Saves the data for this tree to the inputed xml entry.
        
        :param      xml | <xml.etree.ElementTree.Element>
        
        :return     <bool> success

def saveXml(self, xml):
        """
        Saves the data for this tree to the inputed xml entry.
        
        :param      xml | <xml.etree.ElementTree.Element>
        
        :return     <bool> success
        """
        if xml is None:
            return False
        
        # save order data
        xml.set('headerState', str(self.header().saveState().toBase64()))
        xml.set('sortColumn', str(self.sortColumn()))
        xml.set('sortOrder', str(int(self.sortOrder())))
        xml.set('sortingEnabled', str(self.isSortingEnabled()))
        
        return True