##############
## GET TREE ##
##############

$tree = $em->createQuery('SELECT l FROM Entity\Location l ORDER BY l.lft ASC')->getResult();

$result = TreeHelper::getOptions($tree);


#################
## TREE HELPER ##
#################

<?php
namespace Helper;

class TreeHelper
{
    public static function getUL($tree = array())
    {
        $result = '';
        $depth = -1;
        while (!empty($tree)) {
            $node = array_shift($tree);

            if ($node->getLvl() > $depth) {
                $result .= '<ul>';
            }

            if ($node->getLvl() < $depth) {
                $result .= str_repeat('</ul>', $depth - $node->getLvl());
            }

            $result .= '<li>' . $node->getTitle() . '</li>';

            $depth = $node->getLvl();

            if (empty($tree)) {
                $result .= str_repeat('</ul>', $depth + 1);
            }
        }

        return $result;
    }

    public static function getOptions($tree = array())
    {
        $options = $reference = array();
        $depth = -1;
        $parent = null;

        while (!empty($tree)) {
            $node = array_shift($tree);

            $parent = &$options[$node->getUrl()];

            $parent_id = null !== $node->getParent() ? $node->getParent()->getUrl() : 0;

            if ($node->getLvl() == 0) {
                $list[$node->getUrl()] = &$parent;
            } else {
                $options[$parent_id][$node->getUrl()] = &$parent;
            }

        }

        return $options;
    }
}


############
## RESULT ##
############

Array
(
    [usa] => Array
        (
            [california] => Array
                (
                    [san-diego] =>
                    [los-angeles] =>
                    [san-francisco] =>
                )

        )

    [california] => Array
        (
            [san-diego] =>
            [los-angeles] =>
            [san-francisco] =>
        )

    [san-diego] =>
    [los-angeles] =>
    [san-francisco] =>
)


##############
## QUESTION ##
##############

I'm almost getting the desired result set that I want.  My getUL method works, but now I need to grab put the data into an array.  I'm needing something more along the lines of what's below:

Array
(
    [usa] => Array
        (
            [california] => Array
                (
                    [san-diego] =>
                    [los-angeles] =>
                    [san-francisco] =>
                )

        )
)

I will also be needing to expand on this so that I can do (unlimited parent / child levels):

Array
(
        [usa] => Array
        (
            [california] => Array
                (
                    [san-diego] =>
                    [los-angeles] => Array
                        (
                            [north] =>
                            [west] =>
                        )
                    [san-francisco] =>
                )

        )
    [mexico] => Array
        (
            [cabo-san-lucas] =>
            [cancun] =>
        )
)