Bunun funcla alakası yok, cssden listelenen wordpress menüyü dropdowna çevirmen gerek.

#menu, #menu ul { 
    list-style: none; 
    margin: 0; 
    padding: 0; 
    float: left;
    width: 643px;
    height: 35px;
	z-index:100;
}
#menu li { 
    float: left; 
    position: relative;  
    height: 55px;
    padding-top: 34px;
    padding-left: 17px;
    padding-right: 17px;
}

#menu li ul { 
    display: none; 
    position: absolute; 
    top: 19px;
    left: 0; 
}
#menu li > ul { 
top: auto;
left: 0px;
width: 124px;
padding-left: 18px;
float: left;
background: white;
height: auto;
padding-bottom: 5px;
padding-top:5px;
	
}

#menu li a { 
    font: 14px arial, helvetica, sans-serif; 
    display: block;    
    margin: 0; 
    padding: 2px 3px; 
    color: #262727;  
    text-decoration: none; 
}
#menu li a:hover { 
    color: #1b6b00; 
}
#menu li:hover ul { 
    display: block; 
}
#menu li:hover ul, #menu li.over ul{ 
    display: block; 
}

#menu ul li ul li { 
width:120px;
background:none;
float:none;
height:13px;
padding:0px;
padding-bottom:4px;
padding-top:4px;
border-top:1px solid #eaeaea;}

ul.children { 
width: 124px;
float:left;
margin: 0;
background: #fff;
margin-left: -9px;
padding-left: 6px;
padding-bottom:10px;}

Menüyü sıralamak için de

<?php $args = array(
	'show_option_all'    => '',
	'orderby'            => 'name',
	'order'              => 'ASC',
	'style'              => 'list',
	'show_count'         => 0,
	'hide_empty'         => 1,
	'use_desc_for_title' => 1,
	'child_of'           => 0,
	'feed'               => '',
	'feed_type'          => '',
	'feed_image'         => '',
	'exclude'            => '',
	'exclude_tree'       => '',
	'include'            => '',
	'hierarchical'       => 1,
	'title_li'           => __( '' ),
	'show_option_none'   => __(''),
	'number'             => null,
	'echo'               => 1,
	'depth'              => 2,
	'current_category'   => 0,
	'pad_counts'         => 0,
	'taxonomy'           => 'category',
	'walker'             => null
); ?>
<?php wp_list_categories( $args ); ?>