How to upload bulk customer invoices in File Input

Hi

Currently i am working on uploading customer invoice request xml file in File Input under Application and user management workcenter and its successfully creates Invoice request in Customer Invoicing-->Invoice request. But the issue is its only allows me to create uppermost Invoice entry from xml. When i process one xml with one customer invoice request then it works fine but when i add multiple customer invoice requests nodes then it creates invoice of very first node. How can i create multiple invoice requests in one go using single xml file.