using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var node0_1 = new Node { Id = Guid.NewGuid().ToString(), Text = "Node 0-1" };

        var node0_2 = new Node { Id = Guid.NewGuid().ToString(), Text = "Node 0-2" };

        var node1_1 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 1-1", Parent = node0_1 };

        node0_1.Children.Add(node1_1);

        var node1_2 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 1-2", Parent = node0_1 };

        node0_1.Children.Add(node1_2);

        var node2_1 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 2-1", Parent = node0_2 };

        node0_2.Children.Add(node2_1);

        var node2_2 = new Node { Id = Guid.NewGuid().ToString(), Text = "Item 2-2", Parent = node0_2 };

        node0_2.Children.Add(node2_2);

        var result = new List<Node>

        {

            node0_1,

            node0_2

        };

        var output = JsonConvert.SerializeObject(result, new JsonSerializerSettings{

            ReferenceLoopHandling = ReferenceLoopHandling.Ignore

        });

        Console.WriteLine(output);

    }

}

​

public class Node

{

    public Node()

    {

        Children = new List<Node>();

    }

    public string Id {get;set;}

    public string Text { get; set; }

    public string ParentId { get; set; }

    public virtual Node Parent { get; set; }

    public virtual ICollection<Node> Children { get; set; }

}