Chand,
If you notice the BOL model you would be able to see the hierarchy.
Under BTAdminH, we have BTHeaderPartnerSet (BOL Object BTPartnerSet) and under BTHeaderPartnerSet we have BTPartnerAll (BOL Object BTPartner).
So use the method get parent from BTPartner entity to fetch BTPartnerAll and use it again to get BTAdminH entity.
Hope this helps.