Our data 

INSERT INTO comment (
    comment_id, thread_id, parent_comment_id, text, score
)
VALUES
    (1,1,NULL,'Comment from earlier thread',4),
    (2,1,1,'Reply to comment from earlier thread',2),
    (3,2,NULL,'Crap comment that nobody wants to read',0),
    (4,2,NULL,'Top comment',19),
    (5,2,4,'Earliest reply to top comment',6),
    (6,3,NULL,'Comment from later thread',2),
    (7,2,NULL,'Less highly rated comment',3),
    (8,2,4,'Top reply to top comment',22),
    (9,2,8,'Meh response to top reply',1),
    (10,2,7,'Reply to less highly rated comment',5),
    (11,2,8,'Top response to top reply',12);