How do I define hierarchy on OCSV data generated from SQL Server database?

I am pulling data from an SQL server DB, passing it through the compressor before outputting to the report. It is working fine but the challenge is that I want to group some of the fields as hierarchy. How do I achieve this? Find below a snippet of my code.
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            cmd.CommandType = CommandType.StoredProcedure;           
            cmd.Parameters.Add(new SqlParameter("@module", module));            
            DbDataReader dataReader = cmd.ExecuteReader();

            // get compressed stream
            Stream inputStream = Flexmonster.Compressor.Compressor.CompressDb(dataReader);

            // return streaming response
            HttpResponseMessage response = Request.CreateResponse();
            response.Content = new PushStreamContent((Stream outputStream, HttpContent content, TransportContext context) =>
            {
                int count = 0;
                byte[] buffer = new byte[1024];
                while ((count = inputStream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    outputStream.Write(buffer, 0, count);
                    outputStream.Flush();
                }
                outputStream.Close();
            }, new MediaTypeHeaderValue("application/ocsv"));
            //}, new MediaTypeHeaderValue("text/plain"));
            return response;
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