add a submenu

def add(self, items):
        '''add a submenu'''
        if not isinstance(items, list):
            items = [items]
        for m in items:
            updated = False
            for i in range(len(self.items)):
                if self.items[i].name == m.name:
                    self.items[i] = m
                    updated = True
            if not updated:
                self.items.append(m)