Sort by multiple columns using get_posts

$args = array(
    'post_type' => 'event',
    'meta_key' => 'start_date',
    'meta_type' => 'DATE',
    'orderby' => array(
        'start_date' => 'ASC',
        'menu_order' => 'ASC',
    )
);

$posts = get_posts( $args );