using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Node parent = new Node();

        parent.AddChild(new Node());

        parent.AddChild(new Node());

/*      Node firstChild = new Node(parent);

        Node secondChild = new Node(parent);*/

        //Node grandChild = new Node(secondChild);

        foreach(Node child in parent.Children) 

        {

            Console.WriteLine("Child ID: {0}", child.NodeId);

        }

    }

}

​

public class Node 

{

    private ICollection<Node> _children 

    {

        get; 

        set; 

    }

    public Node() 

    {

        NodeId = Guid.NewGuid();

        _children = new List<Node>();

    }

    public Node(Node parentNode) : this() 

    { 

        ParentNode = parentNode;

    }

    public Guid NodeId { get; private set; }

    public Node ParentNode { get; private set; }

    public void AddChild(Node node) 

    {

        _children.Add(node);

    }

    public ICollection<Node> Children 

    {   

        get 

        { 

            return this._children; 

        } 

    }

}