Multi level sub menu - php

Question

I am trying to create a multi level submenu.
I can display just one sub level menu with this code.
How to increase the code to insert a system with parent id ?
There my code than I am trying to develop.
<style>
* {
margin: 0;
padding: 0;
}
body {
font-family: "Comic Sans MS", cursive;
font-size: 15px;
color: #232323;
}
#head {
background: #f9f9f9;
height: 100px;
padding-top: 15px;
border-bottom: 1px solid #d5dce8;
}
.wrap {
width: 1000px;
margin: 0 auto;
}
#head h1
{
float:left;
}
#head a
{
float:right;
}
input,select
{
width:300px;
height:35px;
}
/* nav menu */
#nav {
margin: 0;
padding: 0;
list-style: none;
border-left: 1px solid #d5dce8;
border-right: 1px solid #d5dce8;
border-bottom: 1px solid #d5dce8;
border-bottom-left-radius: 4px;
-moz-border-radius-bottomleft: 4px;
-webkit-border-bottom-left-radius: 4px;
border-bottom-right-radius: 4px;
-moz-border-radius-bottomright: 4px;
-webkit-border-bottom-right-radius: 4px;
height: 50px;
padding-left: 15px;
padding-right: 15px;
background: #f9f9f9;
}
#nav li {
float: left;
display: block;
background: none;
position: relative;
z-index: 999;
margin: 0 1px;
}
#nav li a {
display: block;
padding: 0;
font-weight: 700;
line-height: 50px;
text-decoration: none;
color: #818ba3;
zoom: 1;
border-left: 1px solid transparent;
border-right: 1px solid transparent;
padding: 0px 12px;
}
#nav li a:hover, #nav li a.hov {
background-color: #fff;
border-left: 1px solid #d5dce8;
border-right: 1px solid #d5dce8;
color: #576482;
}
/* subnav */
#nav ul {
position: absolute;
left: 1px;
display: none;
margin: 0;
padding: 0;
list-style: none;
-moz-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
-o-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
-webkit-box-shadow: 0 1px 3px rgba(0, 0, 0, 0.2);
padding-bottom: 3px;
}
#nav ul li {
width: 180px;
float: left;
border-top: 1px solid #fff;
text-align: left;
}
#nav ul li:hover {
border-left: 0px solid transparent;
border-right: 0px solid transparent;
}
#nav ul a {
display: block;
height: 20px;
line-height: 20px;
padding: 8px 5px;
color: #666;
border-bottom: 1px solid transparent;
text-transform: uppercase;
color: #797979;
font-weight: normal;
}
#nav ul a:hover {
text-decoration: none;
border-right-color: transparent;
border-left-color: transparent;
background: transparent;
color: #4e4e4e;
}
</style>
<script type="text/javascript">
$(document).ready(function()
{
$('#nav li').hover(function()
{
$('ul', this).slideDown('fast');
}, function()
{
$('ul', this).slideUp('fast');
});
});
</script>
<div class="wrap">
<ul id="nav">
<?php
// Select all entries from the menu table
$Qmenus = $Db->prepare('SELECT a.id,
a.link,
a.parent,
a.class,
a.sort_order,
amd.label
FROM :table_administrator_menu a,
:table_administrator_menu_description amd
where a.id = amd.id
and amd.language_id = :language_id
ORDER BY a.parent,
a.sort_order
');
$Qmenus->bindInt(':language_id', $OSCOM_Language->getId());
$Qmenus->execute();
while($Qmenus->fetch()){
?>
<li class="<?php $Qmenus->value('class'); ?>"><?php echo $Qmenus->value('label'); ?>
<?php
// Select all entries from the menu table
$QsubMenus = $Db->prepare('SELECT sm.id,
sm.link,
sm.parent,
sm.class,
smd.label,
sm.sort_order
FROM :table_administrator_sub_menu sm,
:table_administrator_sub_menu_description smd
where sm.sub_menu_id = smd.sub_menu_id
and smd.language_id = :language_id
order by sm.parent,
sm.sort_order
');
$QsubMenus->bindInt(':language_id', $OSCOM_Language->getId());
$QsubMenus->execute()
?>
<ul>
<?php
while($QsubMenus->fetch()) {
?>
<li class="<?php $QsubMenus->value('class'); ?>"><?php echo $QsubMenus->value('label'); ?></li><?php
}
?>
</ul>
</li>
<?php
}
?>
</ul>
</div>