Department::getHeadDepartmentId

static function getHeadDepartmentId(int $departmentId, array $departmentTree)
{
	foreach ($departmentTree as $headDepartmentId => $subDepartments)
	{
		foreach ($subDepartments as $subDepartmentId)
		{
			if ((int)$subDepartmentId === $departmentId)
			{
				return $headDepartmentId;
			}
		}
	}

	return null;
}