aggregation in SQL query

Hi all,
I would like to aggregate the result of a hierarchical query.

Here is the query :

SELECT level,
decode(pdt_niv,5,pdt_cod,null) as niv5,
decode(pdt_niv,4,pdt_cod,null) as niv4,
decode(pdt_niv,3,pdt_cod,null) as niv3,
decode(pdt_niv,2,pdt_cod,null) as niv2,
decode(pdt_niv,1,pdt_cod,null) as niv1
from pdt
connect by pdt_cod =prior pdt_per_cod
start with pdt_niv=5

Here is the result :

LEVEL NIV5 NIV4 NIV3 NIV2 NIV1

1 F203
2 RG11
3 TPAP
4 TMAT
5 TPHR
1 F206
2 RG11
3 TPAP
4 TMAT
5 TPHR
1 P005
2 F307
3 TPAP
4 TMAT
5 TPHR

Here is the result I need :

NIV5 NIV4 NIV3 NIV2 NIV1

F203 RG11 TPAP TMAT TPHR
F206 RG11 TPAP TMAT TPHR
P005 F307 TPAP TMAT TPHR

Any idea ?
Any help would be appreciated ...
Thanks a lot in advance !