WITH t AS
(
SELECT 'A' cd, '' pcd FROM dual
UNION ALL SELECT 'B' , 'A'  FROM dual
UNION ALL SELECT 'C' , 'B'  FROM dual
UNION ALL SELECT 'D' , 'C'  FROM dual
UNION ALL SELECT 'E' , 'D'  FROM dual
UNION ALL SELECT 'F' , 'E'  FROM dual
UNION ALL SELECT 'D1', 'C'  FROM dual
UNION ALL SELECT 'E1', 'D1' FROM dual
UNION ALL SELECT 'F1', 'E1' FROM dual
)
SELECT LPAD('-', lv, '-')||lv path
     , cd
  FROM (-- 0. 개층 구조 전개
        SELECT cd, pcd
             , LEVEL lv
             , CONNECT_BY_ISLEAF lf
          FROM t
         START WITH pcd IS NULL
         CONNECT BY PRIOR cd = pcd
        )
 START WITH lf = 1               -- 1. Leaf Node 로부터
 CONNECT BY cd = PRIOR pcd       -- 2. 계층 역 전개 후
 ORDER BY CONNECT_BY_ROOT cd, lv -- 3. 재정렬
;