How to group parent value by child value in BI Publisher?

I have a requirement where I have to group a parent value by its child value but I wonder if this is even possible. I know how to group by a parent value level but I've never done this before.

Any help or idea is welcome.

My expected output would be like: 

Supplier: Bernardo Quintana

Line | Item

1      MP000233

2      MP000129

rnardoItem  Quintana Bernardo Quintana

I attach the file which I'm working with and also the RTF.

<RequisitionLineVO>         <RequisitionLineVORow>            <LineNumber>1</LineNumber>            <ItemDescription>MP000233</ItemDescription>            <RequisitionLineDetailVO>               <RequisitionLineDetailVORow>                    <RequisitionLineId>30009</RequisitionLineId>                    <Supplier>Bernardo Quintana</Supplier>               </RequisitionLineDetailVORow>            </RequisitionLineDetailVO>        </RequisitionLineVORow>         <RequisitionLineVORow>            <LineNumber>2</LineNumber>            <ItemDescription>MP000129</ItemDescription>            <RequisitionLineDetailVO>               <RequisitionLineDetailVORow>                    <RequisitionLineId>30010</RequisitionLineId>                   <Supplier>Bernardo Quintana</Supplier>               </RequisitionLineDetailVORow>            </RequisitionLineDetailVO>