Regarding the following query from a related post: Collapse vertex rows into nested table type (aggregated by ID)

WITH cte (id, x, y) as (
  SELECT 1, 100, 101 FROM DUAL UNION ALL
  SELECT 1, 200, 201 FROM DUAL UNION ALL
  SELECT 2, 300, 301 FROM DUAL UNION ALL
  SELECT 2, 400, 401 FROM DUAL UNION ALL
  SELECT 2, 500, 501 FROM DUAL UNION ALL
  SELECT 3, 600, 601 FROM DUAL UNION ALL
  SELECT 3, 700, 701 FROM DUAL UNION ALL
  SELECT 3, 800, 801 FROM DUAL UNION ALL
  SELECT 3, 900, 901 FROM DUAL
)
SELECT id,
       CAST(
         COLLECT(    --