    @Test
    public void addTreeItemSubRepeat() {

        SideMenu sideMenu = new SideMenu();
        sideMenu.addTreeItem("parent1", clickHandler);
        sideMenu.addTreeItem("parent1", "item", clickHandler);
        sideMenu.addTreeItem("parent2", clickHandler);
        sideMenu.addTreeItem("parent2", "item", clickHandler);
        // expect no exception
    }