How to get list of C# object inside another class object

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ASP.NET

MVC4

C#7.0

WCFService

i have to classes .. follows
and i am trying to get list of PtModifer inside the class PModifierGroup. how can i do this ?

public class PtModifer
   {
       public long ProductCode { get; set; }
       public long MID { get; set; }
       public long MGID { get; set; }
       public string Name { get; set; }
       public Nullable<decimal> Price { get; set; }
   }
   public class PModifierGroup
   {
       public long MGID { get; set; }
       public string GroupName { get; set; }
       public Nullable<int> IsRequired { get; set; }
       public string  AllowMultiple { get; set; }
       public List<PtModifer> PtModifer { get; set; }
   }

now i want to get record from these classes in the form of ..

{  
   "AllowMultiple":"1",
   "GroupName":"Fries",
   "IsRequired":0,
   "MGID":20,
   "PtModifer":[  
      {  
         "MGID":20,
         "MID":56,
         "Name":"Sprinkles",
         "Price":0.0000,
         "ProductCode":1
      }
   ]
}

.
. how to do this in wcf

What I have tried:

i have already tried

public List<PModifierGroup>  GetProductModifier(string ProCode)
       {
           int PCode = Convert.ToInt32(ProCode);
           //IEnumerable<PtModifer> PtModifer = new List<PtModifer>();
           long GroupID = -1;
           using (RestroProEntities db = new RestroProEntities())
           {
               var result = (from P in db.ProductsModifierGroups
                             join MG in db.ModifierGroups on P.MGID equals MG.MGID
                             where P.ProductCode == PCode
                             select new PModifierGroup
                             {

                                 MGID = MG.MGID,
                                 IsRequired = P.IsRequired,
                                 AllowMultiple = P.AllowMultiple,
                                 GroupName = MG.Name,
                                 PtModifer = (from PM in db.ProductsModifiers
                                              join m in db.Modifiers on PM.MID equals m.MID
                                              where PM.ProductCode == PCode & PM.MGID==MG.MGID
                                              select new PtModifer
                                              {
                                                  MGID = GroupID,
                                                  MID = m.MID,
                                                  Name = m.Name,
                                                  Price = m.Price
                                              }).ToList()
                             }).ToList();
               return result;

           };
       }