Task::getKeyToSort

private function getKeyToSort($items): string
{
	$keyToSort = 'PARENT_ID';

	foreach ($items as $item)
	{
		if (array_key_exists('PARENT_NODE_ID', $item))
		{
			$keyToSort = 'PARENT_NODE_ID';
			break;
		}
	}

	return $keyToSort;
}