SERIALIZABLE and INSERTs with multiple VALUES

Hi All,

I notice the following oddity:

 =# CREATE TABLE with_pk (i integer PRIMARY KEY);
CREATE TABLE
=# BEGIN;
BEGIN=# INSERT INTO with_pk VALUES (1) ON CONFLICT DO NOTHING;
INSERT 0 1=# INSERT INTO with_pk VALUES (1) ON CONFLICT DO NOTHING;
INSERT 0 0=# END;
COMMIT
=# BEGIN;
BEGIN=# INSERT INTO with_pk VALUES (2), (2) ON CONFLICT DO NOTHING;
ERROR:  could not serialize access due to concurrent update=# END;
ROLLBACK

How are these two transactions different?

Kind Regards,

  Jason Dusek