Get comments with replies

function _get_child_comments( $clauses ) {
    $clauses['where'] .= ' AND comment_parent > 0';
    return $clauses;
}

function get_comments_with_replies( $query ) {
    if ( empty( $query->query_vars['with_replies'] ) ) {
        return;
    }

    remove_filter( 'parse_comment_query', __FUNCTION__ );
    add_filter( 'comments_clauses', '_get_child_comments' );

    $child_comments = get_comments( $query->query_vars );

    remove_filter( 'comments_clauses', '_get_child_comments' );
    add_filter( 'parse_comment_query', __FUNCTION__ );

    $parent_comment_ids = array();

    foreach ( $child_comments as $comment ) {
        if ( ! in_array( $comment->comment_parent, $parent_comment_ids ) ) {
            $parent_comment_ids[] = $comment->comment_parent;
        }
    }

    $query->query_vars['comment__in'] = $parent_comment_ids;
}
add_action( 'parse_comment_query', 'get_comments_with_replies' );

$comments = get_comments( array( 'post_id' => 123, 'with_replies' => true ) );
echo '<pre>'; print_r( $comments ); echo '</pre>';