This is a bit tricky : when you click on the parent node it will allow you to create unlimited sub Node.
Follow the below steps to achive creation of unlimited suborders nodes.
Step1: In OrderRequest rootNode Type "OrderRequest" in DataStructureType property and press Enter
Step1: In OrderRequest rootNode Type "OrderRequest" in DataStructureType property and press Enter
Step2: Select SubOrder Record Node and select "OrderRequest(ComplexType)" from the List
Step3: Select your BizTalk Mapper and select OrderRequest Message and try to expand the SubOrder as many times as you click Suborder ..it creates that many times of child records
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