using System;

using System.Collections.Generic;

using System.Linq;

​

var initialList = new List<ViewModel>

{

    new ViewModel { OuterCaption = "A outer", InnerCaption = "A inner", Caption = "E", Id = 8},

    new ViewModel { OuterCaption = "B outer", InnerCaption = "B inner", Caption = "A", Id = 5},

    new ViewModel { OuterCaption = "A outer", InnerCaption = "B inner", Caption = "A", Id = 12},

    new ViewModel { OuterCaption = "B outer", InnerCaption = "B inner", Caption = "B", Id = 9},

    new ViewModel { OuterCaption = "A outer", InnerCaption = "B inner", Caption = "B", Id = 23},

    new ViewModel { OuterCaption = "B outer", InnerCaption = "C inner", Caption = "A", Id = 10},

    new ViewModel { OuterCaption = "A outer", InnerCaption = "B inner", Caption = "C", Id = 16},

    new ViewModel { OuterCaption = "A outer", InnerCaption = "A inner", Caption = "C", Id = 4},

    new ViewModel { OuterCaption = "A outer", InnerCaption = "A inner", Caption = "D", Id = 7},

    new ViewModel { OuterCaption = "C outer", InnerCaption = "A inner", Caption = "A", Id = 31},

    new ViewModel { OuterCaption = "B outer", InnerCaption = "A inner", Caption = "A", Id = 19},

    new ViewModel { OuterCaption = "B outer", InnerCaption = "A inner", Caption = "B", Id = 20},

    new ViewModel { OuterCaption = "A outer", InnerCaption = "A inner", Caption = "A", Id = 1},

    new ViewModel { OuterCaption = "A outer", InnerCaption = "A inner", Caption = "B", Id = 3}

}.OrderBy(vm => vm.OuterCaption).ThenBy(vm => vm.InnerCaption).ThenBy(vm => vm.Caption);

​

var list = initialList.GroupBy(vm => vm.OuterCaption).ToList();

​

​

foreach (var outerGrouping in list)

{

    Console.WriteLine(outerGrouping.Key);

    Console.WriteLine("~~~~~~~~~~~~~~~~~~");

​

    foreach (var innerGrouping in outerGrouping.GroupBy(vm => vm.InnerCaption))

    {

        Console.WriteLine(innerGrouping.Key);

​

        foreach (var vm in innerGrouping)

        {

            Console.WriteLine("Caption: " + vm.Caption + " Id:" + vm.Id);

        }

​

        Console.WriteLine("------------------");

    }

​

    Console.WriteLine("~~~~~~~~~~~~~~~~~~");

}

​

class ViewModel

{

    public string OuterCaption { get; set; }

    public string InnerCaption { get; set; }

    public string Caption { get; set; }

    public int Id { get; set; }

​

}