How display two columns in Mvc WebGrid with single object

I am new to MVC and I want to display name of a user in two columns in a WebGrid as display below.

Currently the web grid display data in below format.

I am binding my WebGrid with List<string>, list contains username.

My Controller

public ActionResult Index()
{ 
    List<string> userList = new List<string>();
    userList.Add("User1");
    userList.Add("User2");
    userList.Add("User3");
    userList.Add("User4");
    return View(userList);
}

My Cshtml

@using (Html.BeginForm())
{
    var grid = new WebGrid(Model);
    @grid.GetHtml(columns: grid.Columns(grid.Column(format: (item) => item)));
}