How do I parse non duplicate values in XML to be parsed to database in an XML file which has duplicate records

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XML

SQL

stored-procedure

I have an C# asp page, which has an upload button to upload xml file:
Then I can choose the xml and display in grid view, which is working fine,
and whenever I upload a file which has been already uploaded, it rejects the xml file with duplicate records validation.
But I want to add the non duplicate values which exists in a xml which has duplicate records.
Now when i upload an xml file which has 'a''b''c' , and when i upload another xml which has values 'a''b''c','d''e''f', the whole xml is not getting added and shows error duplicate validation.

What I have tried:

I have a sproc where i use the 'IF EXISTS condition' where x=x,y=y,z=z,then error else add