Multiple emails from a Form

I have a Form that sends data to an e-mail.  How can I add up to 10 email addresses? The code for sending the email is as follows:
                try
                {
                                msg = new MailMessage(txt_Email.Text,
                                                "sec@1stSigBdeAssy.net", "From: 1st Sigbal Brigade Association",
      &nb ...