Build tree from flat array

tree.php

<?php
$elements = array(
	array(
		'id' => 1,
		'parent_id' => null,
		'info' => array('data' => '')
	),
	array(
		'id' => 2,
		'parent_id' => 1,
		'info' => array('data' => '')
	),
	array(
		'id' => 6,
		'parent_id' => 1,
		'info' => array('data' => '')
	),
	array(
		'id' => 4,
		'parent_id' => 6,
		'info' => array('data' => '')
	),
	array(
		'id' => 3,
		'parent_id' => 2,
		'info' => array('data' => '')
	),
	array(
		'id' => 10,
		'parent_id' => null,
		'info' => array('data' => '')
	),
	array(
		'id' => 11,
		'parent_id' => 10,
		'info' => array('data' => '')
	)
);

$result = buildTree($elements);

print json_encode($result);

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

	foreach ($elements as &$element) {
		if ($element['parent_id'] == $parentId) {
			$children = buildTree($elements, $element['id']);
			if ($children) {
				$element['children'] = $children;
			}
			$branch[] = $element;
			unset($element);
		}
	}
	return $branch;
}