a_list.sql

WITH RECURSIVE tree AS (
  SELECT id, ARRAY[]::INTEGER[] AS ancestors
  FROM test WHERE parent_id IS NULL
 
  UNION ALL
 
  SELECT test.id, tree.ancestors || test.parent_id
  FROM test, tree
  WHERE test.parent_id = tree.id
) SELECT * FROM tree

--test table

id, parent_id
1, NULL
2, 1
3, 1

Result
id, ancestors
1 {}
2 {1}
3 {1}

but I want

id, ancestors
1 {2, 3}
2 {}
3 {}