C#

An unhandled exception of type 'System.AccessViolationException' occurred in Unknown Module.
Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

// required
using System.Collections.Generic;
using System.Collections.ObjectModel;

public class Nodes<T> : ObservableCollection<Node<T>>
{
    public Nodes()
    {
        this.CollectionChanged += Nodes_CollectionChanged;
    }

    public static void Nodes_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        string txt = (e.NewItems[0] as Node<T>).Text;

        Console.WriteLine("{0} {1} {2} {3}", e.Action.ToString(), txt, e.OldStartingIndex.ToString(), e.NewStartingIndex.ToString());
    }

    public void Add(string text)
    {
        Node<T> newNode = new Node<T>(text);
        base.Add(newNode);
    }

    public void Add(T value, string text)
    {
        Node<T> newNode = new Node<T>(text) {Value = value};
        base.Add(newNode);
    }
}

public class Node<T>
{
    public T Value { set; get; }
    public string Text { set; get; }
    public Nodes<T> Nodes { set; get; }

    public Node(string text = "")
    {
        Text = text;
        Nodes = new Nodes<T>();
    }

    public Node(T value, string text = "")
    {
        Value = value;
        Text = text;
        Nodes = new Nodes<T>();
    }
}

// test : Button Click on a Form
private void TestNotification_Click(object sender, EventArgs e)
{
     Nodes<string> TestNodes = new Nodes<string>();
     TestNodes.Add("root");
     TestNodes[0].Nodes.Add("child 1");
     TestNodes[0].Nodes[0].Add("child1 of child1");
}

/* output of the test
Add root -1 0
Add child 1 -1 0
Add child1 of child1 -1 0*/