How do I send API push message with .Net / Parse.com? (C#)

This is my application code for sending push message using PARSE

public static string ParseAuthenticate(string strUserName, string 
{
var httpWebRequest = (HttpWebRequest)WebRequest.Create("https://api.parse.com/1/push");
httpWebRequest.ContentType = "application/json";
httpWebRequest.Headers.Add("X-Parse-Application-Id", "my app id");
httpWebRequest.Headers.Add("X-Parse-REST-API-KEY", "my rest api key"); 
httpWebRequest.Method = "POST";
var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
{
var responseText = streamReader.ReadToEnd();
return responseText;
}
}

Request body
{
    "channels": [
      "test"
    ],
    "data": {
      "alert": "12345"
    }
  } 

Above code where is pass my request parameter(body)? how to frame my request as JSON format? Thanks in advance.Please help me to solve this issue.