select /*+ FIRST_ROWS */ * 
from (select /*+ FIRST_ROWS */ 
tree_version_sid,col1,col2, b.tree_id as tree_code,col5,col6...
from ixrev_index_data a, tree_version b 
where a.tree_version_sid = b.tree_version_sid 
 and a.job_sid = 1 and a.tree_category in ('20','43','23') 
connect by prior a.PPI_INDEX_SID = a.HIGHER_INDEX_SID 
and prior a.tree_version_sid = a.tree_version_sid 
start with a.HIGHER_INDEX_SID is null )

SELECT STATEMENT ()     [NULL] 
 VIEW ()        [NULL] 
  FILTER ()     [NULL] 
   CONNECT BY (WITH FILTERING)  [NULL] 
    NESTED LOOPS ()     [NULL] 
     TABLE ACCESS (FULL)        IXREV_INDEX_DATA 
     TABLE ACCESS (BY INDEX RO  TREE_VERSION 
      INDEX (UNIQUE SCAN)       PK_TREE_VERSION 
    NESTED LOOPS ()     [NULL] 
     NESTED LOOPS ()    [NULL] 
      BUFFER (SORT)     [NULL] 
       CONNECT BY PUMP ()       [NULL] 
      TABLE ACCESS (BY INDEX R  IXREV_INDEX_DATA 
       INDEX (SKIP SCAN)        PK_IXREV_INDEX_DATA 
     TABLE ACCESS (BY INDEX RO  TREE_VERSION 
      INDEX (UNIQUE SCAN)       PK_TREE_VERSION 
    NESTED LOOPS ()     [NULL] 
     TABLE ACCESS (FULL)        IXREV_INDEX_DATA 
     TABLE ACCESS (BY INDEX RO  TREE_VERSION 
      INDEX (UNIQUE SCAN)       PK_TREE_VERSION