Query parents without children

I have a menu table and I am struggling to select all parent-menus without a child.

SELECT  
CASE 
WHEN (SELECT COUNT(1) children
       FROM menu
       WHERE cod_idiom = 'EN'
       START WITH cod_menu_parent = m1.cod_menu
       CONNECT BY PRIOR cod_menu = cod_menu_parent ) = 0 THEN
      cod_menu
END x
FROM menu m1
WHERE m1.isSubMenu = 'T' 

*isSubMen开发者_如何学运维u = 'T' means it might (should) have children which may be a sub-menu or a file.

The idea was to first query all sub-menus, get their menu code and then do a CONNECT BY PRIOR to count its children.

The above query didn't have the expected effect, do you guys have any idea?

SELECT m1.cod_menu
    FROM menu m1
    WHERE NOT EXISTS(SELECT NULL 
                         FROM MENU m2 
                         WHERE m1.cod_menu = m2.cod_menu_parent)
        AND m1.isSubMenu = 'T'