If you are trying to debug error ORA-01436: CONNECT BY loop in user data in

the CONNECT BY sql statements, the following might help you:

ALTER SESSION
   SET "_dump_connect_by_loop_data"=TRUE;

-- execute the CONNECT BY here

Now look in the UDUMP destination for the trace file,
it will contain the problematic IDs which are causing the
infinite loop in the hierarchy.

-OR-

Simply if you want to ignore it, use ‘nocycle’ keyword:

select 
   ...
from
  ...
start with
  somecol = 12345
connect by nocycle
  prior nodeto_col = nodefrom_col;