adding child item with higher line item number as that of parent item in Quote

Hi All,

I have the below requirement. Suppose i have two products

1. RE-A-1800X2-16G-R

2. MX-FPC2

i need to add them at the item level as follows using create_related_entity

item no       higher level item no       product

100                                                 RE-A-1800X2-16G-R

101                  100                          MX-FPC2

102                   100                              (some product)

i am not getting any guid after using create_related_entity with the relation   'BTOrderItemAll'

How to pass the second product as the child item of first one using entities? Please suggest

Regards,

Prathyusha VJ