How to Export data to excel from SSRS Report from Asp.net using C#

protected void btnExcel_Click(object sender, ImageClickEventArgs e)
        {
            ExportReport("Excel");

        }
         
  private void ExportReport(string ReportType)
{

  try
            {

                Warning[] warnings;
                string[] streamids;
                string mimeType;
                string encoding;
                string extension;
                String deviceInfo;
                deviceInfo = "True";
                if (ReportType == "Excel")
                {
                    deviceInfo = "<deviceinfo>" + "<simplepageheaders>True</simplepageheaders>" + "</deviceinfo>";
                }
                else if (ReportType == "pdf")
                {

                    deviceInfo = "<deviceinfo>" + "<simplepageheaders>True</simplepageheaders>" + "</deviceinfo>";
                }

                byte[] bytes = ReportViewer1.ServerReport.Render(
                ReportType, deviceInfo, out mimeType, out encoding, out extension,
                out streamids, out warnings);
                Response.Buffer = true;
                Response.Clear();
                Response.ContentType = mimeType;
                Response.AddHeader("content-disposition", "attachment; filename=" + filename + "." + extension);
                Response.BinaryWrite(bytes);
                Response.Flush();

            }
            catch (System.Exception em)
            {
                Exception inner = em.InnerException;

                while ((inner != null))
                {
                    inner = inner.InnerException;
                }
            }
}