Check if Menu Item is Visible

[IamOnStage]

Hello, I currently have the below code.

But when you click on another menu item, it does not close the open menu item.

Any ideas as I am a jQuery newbie!!!

             $(menuid+' ul.menu li.expanded > a').click(function (event) {    
                 event.preventDefault();
                 if ($(this).siblings('ul').is( ":visible" )){
                 $(this).siblings('ul').slideUp('fast'); 
                 } else {          
                 $(this).siblings('ul').slideDown('fast'); 
             }                      
             });