Output of teppic's answer

comments.sql

CREATE TABLE IF NOT EXISTS comment (
  comment_id   serial primary key,
  original_id  integer,
  text         text,
  upvotes      integer
);

INSERT INTO "public"."comment" ("comment_id", "original_id", "text", "upvotes") VALUES 
('1', NULL, 'Hi.. should be 1', '10'),
('2', NULL, 'Je.. should be 10', '0'),
('3', '1', 'Di.. should be 6', '0'),
('4', '1', 'Si.. should be 2', '7'),
('5', '1', 'Op.. should be 3', '5'),
('6', NULL, 'Op.. should be 8', '2'),
('7', '6', 'Op.. should be 9', '2'),
('8', '5', 'Op.. should be 4', '8'),
('9', '1', 'Op.. should be 5', '3'),
('10', '1', 'Th.. should be 7', '0');

output.csv

query.sql

WITH RECURSIVE comment_tree AS (
    -- First select performed to get top level rows
    SELECT
        comment_id,
        original_id,
        upvotes,
        text,
        0 depth, -- depth in the tree
        ARRAY [comment_id] path -- path to node (used to sort depth-first)
    FROM
        comment
    WHERE
        original_id IS NULL
    UNION
    -- Self referential select performed repeatedly until no more rows are found
    SELECT
        c.comment_id,
        c.original_id,
        c.upvotes,
        c.text,
        ct.depth + 1,
        ct.path || c.comment_id
    FROM
        comment c
        JOIN comment_tree ct ON c.original_id = ct.comment_id
)
SELECT
    *
FROM
    comment_tree
ORDER BY
    path