How Web API Return Nested JSON Values by HttpPost call from database?

I dont have any problems but i don't know how API call data Nested Values

My Web API have Controller, Models and DataAccess that i call by use sql to call data

I want API call JSON Data format similar as below :

[
      {
        "Agent_Code": "123456",
        "Name": "Miss Sara Manger",
        "NickName": "Sara",
        "BirthDay": "19690825",
        "CardID": "9999999999",
        "Address": "870  Goldleaf Lane Lyndhurst NJ New Jersey 07071",
        "Mobile": "000000000",
        "Email": "[email protected]",
        "Bank": [
                      {
                        "AcctName": "Miss Sara Manger",
                        "Acctno": "9999999999",
                        "Bank": "KBANK"
                    }
                ]
        }
    ]

Controller:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace Testdata.APIs
{
    public class DashController : BaseApiController

    {
    [HttpPost]
       public List<Models.AgentDto> TestJSON(Models.CountDashReq model)
            {

                DataAccess.DashDAL dal = new DataAccess.DashDAL();
                List<Models.AgentDto> models = dal.TestJSON(model);

                return models;
            }
}

Model AgentDto And BankDto:

public class AgentDto
    {
        public string Agent_Code { get; set; }
        public string Name { get; set; }
        public string NickName { get; set; }
        public string BirthDay { get; set; }
        public string CardID { get; set; }
        public string Address { get; set; }
        public string Mobile { get; set; }
        public string Email { get; set; }
        public string Bank { get; set; }
    }

    public class BankDto
    {
        public string AcctName { get; set; }
        public string Acctno { get; set; }
        public string Bank { get; set; }
    }

DataAccess:

    public List<Models.AgentDto> TestJSON(Models.CountDashReq model)
    {
        string sql = "[dbo].[tb_Json_Get]";
        List<Models.AgentDto> result = new List<Models.AgentDto>();

        if (model != null)
        {

            List<SqlParameter> reqParam = new List<SqlParameter>();

            //reqParam.Add(new SqlParameter("@usrLogin", model.usrLogin));

            DataSet ds = this.Execute(sql, CommandType.StoredProcedure, reqParam.ToArray(), false);

            if (ds.Tables.Count > 0)
            {
                foreach (DataRow row in ds.Tables[0].Rows)
                {
                    Models.AgentDto paramslist = DataAccessUtility.DataTableExtensions.AsEnumerable<Models.AgentDto>(row);

                    result.Add(paramslist);
                }
            }
        }

        return result;
    }

Please help me to use Case-when Thank you very much