Logic to bring child WBSE total budget on their parent WBS

Dear Experts,

My client has one requirement of customize budget report.

Report painter can not be used as this report data will be connected thru interface for other software.

That team require function module for budget data.

Requirement is similar data for overall budget/actual/commitment/assigned/available similar we get in S_ALR_87013558 report.

I created functional logic to get  budget/actual/commitment from tables by passing object number for WBS but not able to give logic for budget total up to its parent level .

Please suggest the logic to get budget data at parent level and then again parent level to next parent level.

Thanks & Regards

SINGH AKS