public class ReadOnlyObservableTrackingCollection<T> : IReadOnlyList<T>, IDisposable, INotifyCollectionChanged {
    //constructor
    public ReadOnlyObservableTrackingCollection(IEnumerable<T> items);

    protected IEnumerable<T> Items { get; }
    protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs e);
    protected virtual void OnTrackingPropertyChanged(T sender, ChainedPropertyChangedEventArgs<object> e);

    public virtual event NotifyCollectionChangedEventHandler? CollectionChanged;
    public virtual event Action<T, ChainedPropertyChangedEventArgs<object>>? TrackingPropertyChanged;

    public IDisposable TrackHandler(Expression<Func<T, object>> property, Action<T, ChainedPropertyChangedEventArgs<object>> handle);

    public TrackingPropertyList<T> CreateTrackingList();
}

public class TrackingPropertyList<T> : IEnumerable<Expression<Func<T,object>>>, IDisposable {

    public void Register(Expression<Func<T, object>> property);
    public void Remove(Expression<Func<T, object>> property);
    public void Clear();
    public void Dispose();

    public IDisposable AttachHandler(Action<T, ChainedPropertyChangedEventArgs<object>> handle);
}

public static void MethodO() {

    var obsList = new ObservableCollection<ObservableItemNode>("ABCD".Select(x => new ObservableItemNode() { Name = x.ToString() }));

    var observer = new ReadOnlyObservableTrackingCollection<ObservableItemNode>(obsList);

    var listener0 = new EventListener<Action<ObservableItemNode, ChainedPropertyChangedEventArgs<object>>>(
        h => observer.TrackingPropertyChanged += h,
        h => observer.TrackingPropertyChanged -= h,
        (s, e) => Console.WriteLine($"Handle All  NodeName:{s.Name}, Property:{e.ChainedName}, Value:{e.PropertyValue.ToString()}"));

    var listener00 = observer.TrackHandler(x => x.Parent.Parent, (s, e) => Console.WriteLine($"Handle GrandParent  NodeName:{s.Name}, Property:{e.ChainedName}, Value:{e.PropertyValue.ToString()}"));

    var obsListTree = obsList.AssembleAsNAryTree(2);
    Console.WriteLine(obsListTree.ToTreeDiagram(x=> x.Name));
    /* 
    Handle All  NodeName:D, Property:Parent.Parent, Value:A
    Handle GrandParent  NodeName:D, Property:Parent.Parent, Value:A
    A
    ├ B
    │ └ D
    └ C
    */

    var trkList1 = observer.CreateTrackingList();
    trkList1.Register(x => x.AdditionalInfo);
    var listener1 = trkList1.AttachHandler((s, e) => Console.WriteLine($"Handle list1  NodeName:{s.Name}, Property:{e.ChainedName}, Value:{e.PropertyValue.ToString()}"));

    var trkList2 = observer.CreateTrackingList();
    trkList2.Register(x => x.AdditionalInfo.Title, x => x.AdditionalInfo.Number);
    var listener2 = trkList2.AttachHandler((s, e) => Console.WriteLine($"Handle list2  NodeName:{s.Name}, Property:{e.ChainedName}, Value:{e.PropertyValue.ToString()}"));

    obsList[3].AdditionalInfo = new AdditionalObj();
    /*
    Handle All  NodeName:D, Property:AdditionalInfo, Value:Title:, Number:0
    Handle list1  NodeName:D, Property:AdditionalInfo, Value:Title:, Number:0
    Handle All  NodeName:D, Property:AdditionalInfo.Title, Value:
    Handle list2  NodeName:D, Property:AdditionalInfo.Title, Value:
    Handle All  NodeName:D, Property:AdditionalInfo.Number, Value:0
    Handle list2  NodeName:D, Property:AdditionalInfo.Number, Value:0
     */

    obsList[3].AdditionalInfo.Title = "Other";
    /*
    Handle All  NodeName:D, Property:AdditionalInfo.Title, Value:Other
    Handle list2  NodeName:D, Property:AdditionalInfo.Title, Value:Other
     */

    var node = new ObservableItemNode() { Name = "E" };
    obsList.Add(node);
    obsListTree.LevelOrder().Last().AddChild(node);
    Console.WriteLine(obsListTree.ToTreeDiagram(x=> x.Name));
    /*
    Handle All  NodeName:E, Property:Parent.Parent, Value:B
    Handle GrandParent  NodeName:E, Property:Parent.Parent, Value:B
    A
    ├ B
    │ └ D
    │   └ E
    └ C
     */

    trkList2.Dispose();
    obsList[3].AdditionalInfo.Number = 5;
    // (no handler)

    //after use
    observer.Dispose();
}