stumped on a with recursive example

on http://wiki.postgresql.org/wiki/CTEReadme

It shows this:

INSERT INTO department (id, parent_department, "name")
VALUES
(0, NULL, 'ROOT'),
(1, 0, 'A'),
(2, 1, 'B'),
(3, 2, 'C'),
(4, 2, 'D'),
(5, 0, 'E'),
(6, 4, 'F'),
(7, 5, 'G');

-- department structure represented here is as follows:
--
-- ROOT-+->A-+->B-+->C
-- | |
-- | +->D-+->F
-- +->E-+->G

I have ran the recursive query and indeed it only is showing A,B,C,D,F and
not E,G as shown in the graphic above. So postgres is understanding the
structure - however I am not.

What I am not getting/seeing is how one is getting the F to come after the
D and the G after the E.

I can see A and E both have a 0 so they branch off of the Null, but why
is the 4,'F' being attached to the 2,'D' and the 5,'G' being attached to
the 0,'E'?