EF Many-to-Many Self-Reference

//Item.cs
    public class Item
    {
        public Item()
        {
            Composites = new HashSet<Item>();
            Components = new HashSet<Item>();
        }

        public int ItemId { get; set; }

        public string Name { get; set; }

        public int Cost { get; set; }

        public virtual ICollection<Item> Composites { get; set; }

        public virtual ICollection<Item> Components { get; set; }

    }

//MyContext.cs
    public class MyContext : DbContext
    {
        public MyContext()
            :base("DbConnection")
        { }

        public DbSet<Item> Items { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Item>()
                .HasMany(x => x.Composites)
                .WithMany(x => x.Components);
        }
    }

//MainWindow.xaml.cs
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            AppDomain.CurrentDomain.SetData("DataDirectory", AppDomain.CurrentDomain.BaseDirectory);
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            Database.SetInitializer<MyContext>(new CreateDatabaseIfNotExists<MyContext>());

            using (MyContext context = new MyContext())
            {
                Item i1 = new Item() { Name = "Motherboard", Cost = 500 };
                Item i2 = new Item() { Name = "Network Adapter", Cost = 150 };
                Item i3 = new Item() { Name = "System Unit", Cost = 250 };

                context.Items.Add(i1);
                context.Items.Add(i2);
                context.Items.Add(i3);

                context.SaveChanges();

                i3.Components.Add(i1);
                i3.Components.Add(i2);
                i1.Composites.Add(i3);
                i2.Composites.Add(i3);

                context.SaveChanges();
            }
        }
    }