Multidimensional array directory map

I'm trying to get a directory structure in a multidimensional array.

I got this far:

function dirtree($dir, $regex = '', $ignoreEmpty = false)
{
    if (!$dir instanceof DirectoryIterator) {
        $dir = new DirectoryIterator((string) $dir);
    }
    $dirs = array();
    $files = array();
    foreach ($dir as $node) {
        if ($node->isDir() && !$node->isDot()) {
            $tree = dirtree($node->getPathname(), $regex, $ignoreEmpty);
            if (!$ignoreEmpty || count($tree)) {
                $dirs[$node->getFilename()] = $tree;
            }
        } elseif ($node->isFile()) {
            $name = $node->getFilename();
            if ('' == $regex || preg_match($regex, $name)) {
                $files[] = $name;
            }
        }
    }
    asort($dirs);
    sort($files);
    return array_merge($dirs, $files);
}

But I am having issues getting the folder name instead of the index 0,1 .etc. This seems to be due to the fact that my directories have numeric names?

Array
(
    [0] => Array  // 0 should be the folder name
        (
            [0] => m_109225488_1.jpg
            [1] => t_109225488_1.jpg
        )

    [1] => Array
        (
            [0] => m_252543961_1.jpg
            [1] => t_252543961_1.jpg
        )