Connect by is leaf , level ,start with in postgresql

Question

enter image description hereenter image description hereUnable to migrate the merge code that contains level,connect by prior,start with (in postgresql from oracle).

Code:

MERGE INTO ABC.CUSTOMER CT
 USING (SELECT CUST_NO,
               CUST_HIGH_PARENT_NO,
               CUST_CORP_POS,
               CUST_CORP_SUBS,
               TIMESTAMP,
               LEVEL LVL,
               (SELECT MAX(LEVEL)
                  FROM ABC.CUSTOMER
                 START WITH CUST_NO = CUST_NO
                CONNECT BY PRIOR CUST_PARENT_NO = CUST_NO) MXLVL,
               (SELECT CUST_NO
                  FROM ABC.CUSTOMER
                 WHERE CONNECT_BY_ISLEAF = 1
                 START WITH CUST_NO = CUST_NO
                CONNECT BY PRIOR CUST_PARENT_NO = CUST_NO) HIGHPARENT
          FROM ABC.CUSTOMER
         START WITH CUST_NO = CUST_NO
        CONNECT BY PRIOR CUST_PARENT_NO = CUST_NO) A
 ON (UPC.CUST_NO = A.CUST_NO)
 WHEN MATCHED THEN
   UPDATE
      SET 
              CUST_CORP_SUBS = (SELECT COUNT(*) - 1
                                      FROM ABC.CUSTOMER
                                     START WITH CUST_NO =
                                                CT.CUST_NO
                                    CONNECT BY PRIOR CUST_NO =
                                                CUST_PARENT_NO),
          CUST_CORP_POS    = A.MXLVL - A.LVL,
          CUST_HIGH_PARENT_NO= HIGHPARENT,
          TIMESTAMP              = SYSDATE; 

I've

Tried below but unable to it fully. I need help.

Use recursive cte ,tried to use update ,subquery ,level.

Postgresql Code: The oracle query merging two rows in a database.

UPDATE ABC.CUSTOMER CT
      SET  CUST_PAYOR_SUBS = (SELECT COUNT(*) 
                                 FROM ABC.CUSTOMER
                                    (WITH RECURSIVE CUST AS
      (SELECT COUNT(*) FROM ABC.CUSTOMER WHERE CUST_NO = CT.CUST_NO
         UNION ALL 
         SELECT COUNT(*) FROM ABC.CUSTOMER C ,ABC.CUSTOMER CUST
             WHERE C.CUST_NO = CUST.CUST_PAYOR_NO)
             SELECT COUNT(*)
             FROM ABC.CUSTOMER CUST),
      CUST_PAYOR_POS    = A.MXLVL - A.LVL,
      CUST_HIGH_PAYOR_NO = A.HIGHPAYOR,
      TIMESTAMP             = CURRENT_TIMESTAMP::TIMESTAMP(0)
      FROM 
          (WITH RECURSIVE CTE AS
      (SELECT CUST_NO,
           CUST_HIGH_PAYOR_NO,
           CUST_PAYOR_POS,
           CUST_PAYOR_SUBS, 1 as level
       FROM ABC.CUSTOMER 
       WHERE CUST_NO = '00009'---UPC.CUST_NO
         UNION ALL 
         SELECT C.CUST_NO,
           C.CUST_HIGH_PAYOR_NO,
           C.CUST_PAYOR_POS,
           C.CUST_PAYOR_SUBS,
           C.level+1
       FROM CTE C
       JOIN ABC.CUSTOMER CUST ON C.CUST_NO = CUST.CUST_PAYOR_NO)
        SELECT * FROM CTE) MXLVL,
      WHERE UPC.CUST_NO = A.CUST_NO