如何构造树状 JSON 数据 JSON-Tree

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace DFS
{
    class Program
    {
        static void Main(string[] args)
        {
            List<HelloChinaModel> MList = new List<HelloChinaModel>()
            {
                new HelloChinaModel(){ Id=1,Province="河南省",City="商丘市",District="永城市",OrgName="薛湖镇",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="河南省",City="商丘市",District="夏邑县",OrgName="火店乡",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="河南省",City="商丘市",District="睢阳区",OrgName="龙华小区",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="河南省",City="平顶山市",District="新华区",OrgName="河南城建学院",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="河南省",City="平顶山市",District="鲁山县",OrgName="炉山镇",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="河南省",City="洛阳市",District="阳逻县",OrgName="大杨镇",AddTime=DateTime.Now},

                new HelloChinaModel(){ Id=1,Province="江苏省",City="苏州市",District="张家港市",OrgName="乐余镇",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="江苏省",City="苏州市",District="昆山市",OrgName="小上海镇",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="江苏省",City="南京市",District="雨花台区",OrgName="雨花台小区",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="江苏省",City="徐州市",District="沛县",OrgName="王文学镇",AddTime=DateTime.Now},

                new HelloChinaModel(){ Id=1,Province="山东省",City="日照市",District="花果山县",OrgName="猴子镇",AddTime=DateTime.Now},
                new HelloChinaModel(){ Id=1,Province="山东省",City="青岛市",District="青岛啤酒县",OrgName="扎啤镇",AddTime=DateTime.Now},
            };
            // 首先根据省份分组
            var P_ls = MList.GroupBy(a =>  a.Province ).Select(g => (new { Province = g.Key, Citys = g })).ToList();//省份列表
            //
             List<Model_P> PList = new List<Model_P>();
            foreach (var item in P_ls)
            {
                Model_P P = new Model_P();
                //
              
                //
                List<Model_C> CList = new List<Model_C>();
                //获取各个分组
                var Province = item.Province;//省份的名称
                var CitysList = item.Citys;//省份对应的市 列表
                var C_ls = CitysList.GroupBy(a => a.City ).Select(g => new { City = g.Key, Districts = g }) ;//市/区列表
                foreach (var Citem in C_ls)
                {
                    List<Model_D> DList = new List<Model_D>();
                    Model_C C = new Model_C();
                    //
                    var DistrictsLsit = Citem.Districts;//
                    var D_ls = DistrictsLsit.GroupBy(a => a.District ).Select(g => new { Districts = g.Key, OrgNames = g });//县/区列表
                    foreach (var Ditem in D_ls)
                    {
                        List<Model_O> OList = new List<Model_O>();
                        Model_D D = new Model_D();
                      
                        var OrgNamesList = Ditem.OrgNames.ToList();
                        var O_ls = OrgNamesList.GroupBy(a =>a.OrgName ).Select(g => new { OrgName = g.Key });//乡镇列表/没有下级了
                       
                        foreach (var Oitem in O_ls)
                        {
                           
                            Model_O O = new Model_O();
                            string orgName = Oitem.OrgName.ToString();
                            O.OrgName = orgName;
                            OList.Add(O);
                            D.nodes = OList;
                        }
                        string Dname = Ditem.Districts.ToString();
                        D.District = Dname;

                        DList.Add(D); C.nodes = DList;
                    }
                    string Cname = Citem.City.ToString();
                   
                    C.City=Cname;
                    CList.Add(C); 
                    P.nodes = CList;
                }
                P.Province = item.Province.ToString();
               
                PList.Add(P);
            }
            string Json = JsonConvert.SerializeObject(PList);
            Console.WriteLine(Json);

            Console.ReadKey();
        }
    }

    public partial class HelloChinaModel
    {
        public int Id { get; set; }
        public string Province { get; set; }
        public string City { get; set; }
        public string District { get; set; }
        public string OrgName { get; set; }
        public Nullable<System.DateTime> AddTime { get; set; }
    }

    /// <summary>
    /// 省
    /// </summary>
    public class Model_P
    {
        public string Province { get; set; }
        public List<Model_C> nodes { get; set; }
    }
    /// <summary>
    /// 市/区
    /// </summary>
    public class Model_C
    {
        public string City { get; set; }
        public List<Model_D> nodes { get; set; }
    }
    /// <summary>
    /// 县(县级市)/区
    /// </summary>
    public class Model_D
    {

        public string District { get; set; }
        public List<Model_O> nodes { get; set; }
    }
    /// <summary>
    /// 镇/乡/其他
    /// </summary>
    public class Model_O
    {
        public string OrgName { get; set; }
    }

}