Functional Module for BOM

Hi Gurus,

I would like to know is there any functional module by which we can read the Zeroth level of BOM from a child level mterial.

it is Like BOM Implosion

from child to parent.

For example i have the bom like below

0 level--- FERT

1 LVEL-- HALB1

2 LEVEL-HALB2

3 LEVEL-ROH

In this structure i know the ROH MATNR.Now i have to get the FERT MATNR.

Suggest me is there anyother way to find it.