function clickMenu (menuGroup) {
   while (menuGroup.nextSibling) {
        menuGroup = menuGroup.nextSibling;
        // toggle display of level 2 menus
        if (menuGroup.nodeName=='TR') {
           if (menuGroup.style.display=='none') {
               menuGroup.style.display='';
           }
           else {
               menuGroup.style.display='none';
           }
        }
   }
}