Hello tarney,

In order to disable all root nodes in WebDataMenu, something similar to the following may be used:

            function disableRootNodes() {
                var menu = $find("<%= WebDataMenu1.ClientID %>");
                for (i = 0; i < menu.getItems().get_length() ; i++) {
                    menu.getItems().getItem(i).set_enabled(false);
                }
            }

Hope this helps. Please do not hesitate to contact me if you have any questions.