C# program creates file from serialize, I want to save it

Stream xmlfile = File.OpenWrite("current.xml");

X12Parser parser = new X12Parser();
Interchange interchange = parser.Parse(inputStream);

String xml = interchange.Serialize();
inputStream.Seek(0,0);

       CopyStream(inputStream.BaseStream, xmlfile);
       xmlfile.Close();
...
public static void CopyStream(Stream input, Stream output)
       {
       byte[] buffer = new byte[8 * 1024];
       int len;
       while ( (len = input.Read(buffer, 0, buffer.Length)) > 0)
          {
          output.Write(buffer, 0, len);
          }
       }