TABLE A 의

A A1 1

A A2 2

A A3 3

B B1 1

이 부분이 잘 못 적으신거라면

 A1 A 1

A2 A 2

A3 A 3

B1 B 1   이 맞다면

그냥   union all  해서 하시면 되겠는데요?

WITH a AS
(
SELECT 'A' id, '0' p_id, 1 ord FROM dual
UNION ALL SELECT 'B' , '0', 1 FROM dual
UNION ALL SELECT 'C' , '0', 1 FROM dual
UNION ALL SELECT 'A1', 'A', 1 FROM dual
UNION ALL SELECT 'A2', 'A', 2 FROM dual
UNION ALL SELECT 'A3', 'A', 3 FROM dual
UNION ALL SELECT 'B1', 'B', 1 FROM dual
)
, b AS
(
SELECT 'A' id, 'A1' p_id, 1 ord FROM dual
UNION ALL SELECT 'B', 'A1', 2 FROM dual
UNION ALL SELECT 'C', 'A3', 1 FROM dual
)
, c AS
(
SELECT id, p_id, ord FROM a
UNION ALL
SELECT '@' || id id, p_id, ord FROM b
)
SELECT LPAD(' ', (LEVEL-1)*2, ' ') || LTRIM(id, '@') id
  FROM c
 START WITH p_id = '0'
 CONNECT BY PRIOR id = p_id
;