Categoriy.cs

public class Cate
{
    public int Id { get; set; }
    public int? ParentId { get; set; }
    public string Name { get; set; }
}

var cats = new List<Cate> 
{
      new Cate {
          Id = 1, ParentId = null, Name = "First"
      }, new Cate {
          Id = 2, ParentId = null, Name = "Second"
      }, new Cate {
          Id = 3, ParentId = null, Name = "Thrid"
      }, new Cate {
          Id = 4, ParentId = null, Name = "Fourth"
      }, new Cate {
          Id = 5, ParentId = 4, Name = "SubFourth1"
      }, new Cate {
          Id = 6, ParentId = 4, Name = "SubFourth2"
      }, new Cate {
          Id = 7, ParentId = 5, Name = "Sub_SubFourth1"
      }, new Cate {
          Id = 8, ParentId = null, Name = "Sixth"
      }, new Cate {
          Id = 9, ParentId = null, Name = "Seventh"
      }, new Cate {
          Id = 10, ParentId = 9, Name = "SubSeventh1"
      }, new Cate {
          Id = 11, ParentId = 9, Name = "SubSeventh2"
      }, new Cate {
          Id = 12, ParentId = null, Name = "Eighth"
      }, new Cate {
          Id = 13, ParentId = null, Name = "Ninth"
      }, new Cate {
          Id = 14, ParentId = null, Name = "Tenth"
      }, new Cate {
          Id = 15, ParentId = null, Name = "Eleventh"
      }, new Cate {
          Id = 16, ParentId = 15, Name = "SubEleventh"
      }, new Cate {
          Id = 17, ParentId = 16, Name = "Sub_SubEleventh"
      }
 };