Oracle 11g Release 2

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create table temp(id, parent, child) as (
  select 1,   100,  1001 from dual union all
  select 2,   100,  1002 from dual union all
  select 3,   100,  1003 from dual union all
  select 4,  1001, 10011 from dual union all
  select 5, 10011, 10012 from dual union all
  select 6,  1002, 10022 from dual union all
  select 7,  1002, 10023 from dual );

7 rows affected

    select 0 id, '100' child, 0 lvl from dual
    union all
    select id, lpad(' ', 4 * level ) || child, level 
      from temp
      start with parent = 100
      connect by  parent = prior child;



ID
CHILD
LVL


0
100
0

1
    1001
1

4
        10011
2

5
            10012
3

2
    1002
1

6
        10022
2

7
        10023
2

3
    1003
1


    with c(id, child, lvl) as (
        select 0, '100', 0 from dual 
        union all
        select t.id, lpad(t.child, (c.lvl + 2) * 4, ' '), c.lvl + 1 
          from c join temp t on t.parent = c.child)
    search depth first by id set seq
    select id, child, lvl from c;



ID
CHILD
LVL


0
100
0

1
    1001
1

4
       10011
2

5
           10012
3

2
    1002
1

6
       10022
2

7
       10023
2

3
    1003
1


    select id, lpad(' ', 4 * (level-1) ) || child child, level 
      from (select id, parent, child from temp union all
            select null, null, 100 from dual )
      start with child = 100
      connect by  parent = prior child;



ID
CHILD
LEVEL


null
100
1

1
    1001
2

4
        10011
3

5
            10012
4

2
    1002
2

6
        10022
3

7
        10023
3

3
    1003
2