Setting hierarchy of the data segments in NCo 3.0

I am trying to Invoke an IDoc Send ( IDOC_INBOUND_ASYNCHRONOUS tRFC call ) by passing IDOC_CONTROL_REC_40 & IDOC_DATA_REC_40 tables using NCo 3.0

I am getting the exception :

"EDI: Syntax error in IDoc (mandatory group missing)".

One reason I could see (WE05 transaction) is that the hierarchy of the data segments is not proper.

How to establish proper parent - child relation between segments using NCo 3.0 code.

Thanks

Ravi