自连接<EntityFramework6.0>

 public class PictureCategory
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int CategoryId { get; private set; }
        public string Name { get; set; }
        public int? ParentCategoryId { get; private set; }
        public virtual PictureCategory ParentCategory { get; set; }
        public virtual ICollection<PictureCategory> SubPictureCategories { get; set; }

        public PictureCategory()
        {
            SubPictureCategories = new HashSet<PictureCategory>();
        }
    }

    public class PictureCategoryContext : DbContext
    {
        public virtual DbSet<PictureCategory> PictureCategories { get; set; }
        public PictureCategoryContext() : base("name=DemoContext") { }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<PictureCategory>()
                .HasKey(p=>p.CategoryId)
                .HasMany(p => p.SubPictureCategories)
                .WithOptional(t => t.ParentCategory)
                .HasForeignKey(t=>t.ParentCategoryId);
        }
    }

private static void Main()
        {
            using (var context = new PictureCategoryContext())
            {
                var _1st = new PictureCategory { Name = "第1代" };
                var _2st = new PictureCategory { Name = "第2代" };
                var _3_1st = new PictureCategory { Name = "第3_1代" };
                var _3_2st = new PictureCategory { Name = "第3_2代" };
                var _3_3st = new PictureCategory { Name = "第3_3代" };
                var _4st = new PictureCategory { Name = "第4代" };
                var _5_1st = new PictureCategory { Name = "第5_5_1代" };
                var _5_2st = new PictureCategory { Name = "第5_2代" };
                _1st.SubPictureCategories = new List<PictureCategory> { _2st };
                _2st.SubPictureCategories = new List<PictureCategory> { _3_1st, _3_2st, _3_3st };
                _3_3st.SubPictureCategories = new List<PictureCategory> { _4st };
                _4st.SubPictureCategories = new List<PictureCategory> { _5_1st, _5_2st };
                context.PictureCategories.Add(_1st);
                context.SaveChanges();
            }

            using (var context=new PictureCategoryContext())
            {
               var query = context.PictureCategories.Where(p=>p.ParentCategory==null).ToList();
               query.ForEach(t => Print(t,1));
            }

            Console.ReadKey();
        }

        private static void Print(PictureCategory category, int level)
        {
            Console.WriteLine("{0}--{1}", category.Name, level);
            category.SubPictureCategories.ToList().ForEach(t=>Print(t,level+1));
        }