UPDATE t SET rate = new.rate
FROM
(
  WITH RECURSIVE cte(id, pid, rate) AS
  (SELECT id,
          pid,
          rate 
    FROM  t a
    UNION ALL
    SELECT cte.id,
           b.pid,
           b.rate * cte.rate / 100
    FROM t b
    INNER JOIN cte ON b.id = cte.pid
)
SELECT id, rate FROM cte WHERE pid = 0
) new
WHERE new.id = t.id;