I want to customze menu_tree output I found a code in drupal page in this url http://api.drupal.org/api/drupal/includes%21menu.inc/function/theme_menu_tree/6#comment-1073

code is 

&lt;?php
function phptemplate_menu_tree($tree,$menu_name="") {
     return '&lt;ul class="menu menu-$menu_name "&gt;'. $tree .'&lt;/ul&gt;';
}
?&gt;


it is written that we can customize every menu by css and also adding $menu_name.

but even though that I have added this function into my template.php and it is working , $menu_name variable is always empty

really the target that I am following is :
I want to modify the css class of the ROOT us base on menu name.

for example for primary links , i want to have this return out put

'&lt;ul class="menu menu-primary-links "&gt;'. $tree .'&lt;/ul&gt;'


or for secondary links i want to have this return output

'&lt;ul class="menu menu-secondary-links "&gt;'. $tree .'&lt;/ul&gt;'


$tree includes all nested li items from the selected menu.

please help me
page.tpl.php

for admin menu

    &lt;?php print '&lt;ul id="nav-admin" class="menu   clearfix"&gt;'.menu_tree($menu_name = 'navigation').'&lt;/ul&gt;';?&gt;

//for primary menu
 &lt;?php print  '&lt;ul id="nav-primary" class="menu clearfix"&gt;'.menu_tree($menu_name = 'primary-links').'&lt;/ul&gt;'; ?&gt;
//for secondary menu
 &lt;?php print  '&lt;ul id="nav-secondary" class="menu clearfix"&gt;'.menu_tree($menu_name = 'secondry-links').'&lt;/ul&gt;'; ?&gt;


template.php


  function menu_tree($tree}{return $tree;}