create table test_connect_by (
  parent     number,
  child      number,
  constraint uq_tcb unique (child)
);

##</code><code>##

insert into test_connect_by values ( 5, 2);
insert into test_connect_by values ( 5, 3);
insert into test_connect_by values (18,11);
insert into test_connect_by values (18, 7);
insert into test_connect_by values (17, 9);
insert into test_connect_by values (17, 8);
insert into test_connect_by values (26,13);
insert into test_connect_by values (26, 1);
insert into test_connect_by values (26,12);
insert into test_connect_by values (15,10);
insert into test_connect_by values (15, 5);
insert into test_connect_by values (38,15);
insert into test_connect_by values (38,17);
insert into test_connect_by values (38, 6);
insert into test_connect_by values (null,38);
insert into test_connect_by values (null,26);
insert into test_connect_by values (null,16);

##</code><code>##

select lpad(' ',2*(level-1)) || to_char(child) s 
  from test_connect_by 
  start with parent is null
  connect by prior child = parent;

##</code><code>##

38
  15
    10
    5
      2
      3
  17
    9
    8
  6
26
  13
  1
  12
16