CREATE TABLE tree (
    node_id     INT,
    parent_id   INT
)

INSERT INTO
  tree
          SELECT    1, NULL FROM DUAL
UNION ALL SELECT    2,    1 FROM DUAL
UNION ALL SELECT    3,    1 FROM DUAL
UNION ALL SELECT    4,    2 FROM DUAL
UNION ALL SELECT    5,    2 FROM DUAL
UNION ALL SELECT    6,    3 FROM DUAL
UNION ALL SELECT    7,    3 FROM DUAL
UNION ALL SELECT    8,    4 FROM DUAL
UNION ALL SELECT    9,    4 FROM DUAL
UNION ALL SELECT   10,    5 FROM DUAL
UNION ALL SELECT   11,    5 FROM DUAL
UNION ALL SELECT   12,    6 FROM DUAL
UNION ALL SELECT   13,    6 FROM DUAL
UNION ALL SELECT   14,    7 FROM DUAL
UNION ALL SELECT   15,    7 FROM DUAL

15 rows affected

SELECT
  node_id, parent_id, level
FROM
  tree
WHERE
  level < 3
CONNECT BY
  PRIOR node_id = parent_id
START WITH
  parent_id = 3
ORDER BY
  level, node_id

| 节点ID|母体ID|水平|
| - ------|- ------|- ------|
| 六个|三个|1个|
| 七|三个|1个|
| 十二|六个|第二章|
| 十三|六个|第二章|
| 十四|七|第二章|
| 十五|七|第二章|
fiddle