Recursive UL Output with name-based array keys

<?php
 
	function recursion($multi_dimensional_array)
	{
		$m = $multi_dimensional_array;
 
		$keys = array();
		foreach($m as $key=>$value)
		{
			$keys[] = $key;
		}
 
		$i = 0;
		while($i < count($multi_dimensional_array))
		{
			echo '<li><a href="#">'.$keys[$i].'</a>';
			if(is_array($multi_dimensional_array[$keys[$i]]))
			{
				echo '<ul>';
				recursion($multi_dimensional_array[$keys[$i]]);
				echo '</ul>';
			}
			echo '</li>';
			$i++;
		}
	}
 
?>
 
Usage Example:
 
<ul>
	<? recursion($array); ?>
</ul>