Can fire a registered event when an item is added to the list.

EventList.cs

using System;
using System.Collections.Generic;

namespace NameSpace
{
    public class EventList<T> : List<T>
    {
        public event EventHandler OnAdd;
        public event EventHandler OnAddRange;
        public event EventHandler OnRemove;

        new public void Add(T item)
        {
            base.Add(item);
            OnAdd?.Invoke(this, new EventListEventArgs<T>
            {
                AddedItem = item
            });
        }

        new public void AddRange(IEnumerable<T> collection)
        {
            base.AddRange(collection);
            OnAddRange?.Invoke(this, new EventListEventArgs<T>
            {
                AddedItems = collection
            });
        }

        new public void Remove(T item)
        {
            base.Remove(item);
            OnRemove?.Invoke(this, new EventListEventArgs<T>
            {
                RemovedItem = item
            });
        }
    }

    public class EventListEventArgs<T> : EventArgs
    {
        public T AddedItem { get; set; }
        public IEnumerable<T> AddedItems { get; set; }
        public T RemovedItem { get; set; }
    }
}