create a List of list

Question

Good evening everyone, I create a class named chien.cs with this code:

 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace formList
{
    class Chien
    {
        private int nombre;
        public int chatte { get { return nombre; } set { nombre = value; } }

        public Chien()
        {
            chatte = 3;

        }
    }
}

 and then I create a custom control with this code:

 

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace formList
{
    public partial class CustomChien : Control
    {
        public CustomChien()
        {
            InitializeComponent();
        }

        protected override void OnPaint(PaintEventArgs pe)
        {
            base.OnPaint(pe);
        }

        private List<Chien> listchien = new List<Chien>();
        public List<Chien> ListItem
        {
            get { return listchien; }
            set
            {
                foreach (Chien item in value)
                {
                    listchien.Add(item);

                }
            }
        }
    }
}

 and then during compiling it shows me this error that I do not understand that to mean.