Función recursiva para construir menú en arreglo mutlidimensional

build_tree.php

<?php

function buildTree(array $elements, $parentId = NULL) {
	$branch = array();

	foreach ($elements as $key => $element) {
		if ($element['parent'] == $parentId) {
			$children = buildTree($elements, $element['id']);
			if ($children) {
				$element['children'] = $children;
			}
			$branch[] = $element;
		}
	}

	return $branch;
}

$rows = array(
			array('id'=>'user', 'label' => 'User', 'parent' => NULL),
			array('id'=>'courses', 'label' => 'Courses', 'parent' => NULL),
			array('id'=>'courses-import', 'label' => 'Courses Import', 'parent' => 'courses'),
		);

echo '<pre>';
$tree = buildTree($rows);

print_r($tree);