expanding a menu

expanding a menu

I am using this menu code in my application:
http://www.mediamilan.com/tutos/how-to-create-simple-tree-structure-menu-using-jquery-and-css/

Modified for my app, of course.
I need to add, mostly for testing purposes because the menu is large, an "expand all" button.

The code for expanding a menu section upon clicking is this:

$(document).ready(function() {
       
    //Class 'contentContainer' refers to 'li' that has child with it.
    //By default the child ul of 'contentContainer' will be set to 'display:none'
       
    $("#treeMenu li").toggle(           
           
        function() { // START FIRST CLICK FUNCTION
              $(this).children('ul').slideDown()
              if ($(this).hasClass('contentContainer')) {  
                  $(this).removeClass('contentContainer').addClass('contentViewing');
                      }
          }, // END FIRST CLICK FUNCTION
                 
          function() { // START SECOND CLICK FUNCTION
              $(this).children('ul').slideUp()

              if ($(this).hasClass('contentViewing')) {
                  $(this).removeClass('contentViewing').addClass('contentContainer');
              }
                } // END SECOND CLICK FUNCTIOn
            ); // END TOGGLE FUNCTION
                   
        }); // END DOCUMENT READY


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My attempt to expand-all is not working:

function expandall() {
var els = document.getElementsByTagName('ul');

for( i = 0; i<els.length; i++) {
    if (els[i].hasClass('contentContainer')) {  
        els[i].children('ul').slideDown(); }
    els[i].removeClass('contentContainer').addClass('contentViewing');
    }
}