using System;

using System.Linq;

using System.Collections;

using System.Collections.Generic;

using System.Xml;

using System.Xml.Linq;

using System.Globalization;

using System.Data;

using System.Data.DataSetExtensions;

using System.Net;

using System.Net.Sockets;                   

using System.IO;

public class Program

{

    public static void Main()

    {

        var inputList = new List<InputClass>();

        inputList.Add(new InputClass() { id = 1, text = "Item #1"});

        inputList.Add(new InputClass() { id = 2, text = "Item #2" });

        inputList.Add(new InputClass() { id = 3, text = "Item #3" });

        inputList.Add(new InputClass() { id = 4, text = "SubItem #1", parentId = 1 });

        inputList.Add(new InputClass() { id = 5, text = "SubItem #2", parentId = 1 });

        inputList.Add(new InputClass() { id = 6, text = "SubItem #3", parentId = 2 });

        inputList.Add(new InputClass() { id = 7, text = "Sub-Sub Item #1", parentId = 4 });

        inputList.Add(new InputClass() { id = 8, text = "Sub-Sub Item #1", parentId = 7 });

        Recursive(inputList,1).Dump();

    }

    public static IEnumerable<InputClass> Recursive(List<InputClass> items, int toplevelid)     

    {

        List<InputClass> inner = new List<InputClass>();

        foreach (var t in items.Where(item=>item.parentId ==toplevelid))

        {

            inner.Add(t);

            inner = inner.Union(Recursive(items, t.id)).ToList();

        }       

        return inner;

    }

}

​

public class InputClass

{

    public int id { get; set; }

    public string text { get; set; }

    public string icon { get; set; }

    public int? parentId { get; set; }

​

}