Problem with Await in File Handle Asp.Net

I created an Webform application which allow user to upload file which using AJAX and FileHandle.ashx in Asp.Net I'm trying to make it run asynchronous but it doesn't work as well. The code below return "StartSavedEnd" which mean await doesn't work since my file take 10second to upload. Any advice? Many thanks

    public override async Task ProcessRequestAsync(HttpContext context)
    {
    context.Response.ContentType = "text/plain";
    context.Response.Write("Start");

    await SaveFile(context);

    context.Response.Write("End");
    }
async Task SaveFile(HttpContext context)
{
    var task = Task.Run(() =>
    {
        if (context.Request.Files.Count > 0)
        {
            HttpFileCollection files = context.Request.Files;
            foreach (string key in files)
            {
                HttpPostedFile file = files[key];
                string fileName = file.FileName;
                fileName = context.Server.MapPath(fileName);
                file.SaveAs(@"C:\TestZip.zip");
                context.Response.Write("Saved");

            }
        }
    });
    await task;
}