array list not add extra modal object when i arraylist.add(modal);

i have an arraylist
public class BookingPassengerDetails
{

    //public int PassengerDetailsId { get; set; }
    public string Title { get; set; }
    public string PaxNo { get; set; }
    public string MobileNo { get; set; }
    public string EmailId { get; set; }
    public string Address { get; set; }
    public string MerchantCode { get; set; }
    public bool GetPasssengerVisibility => !(PaxNo.Contains("1"));
    public string PassengerType { get; set; }
    public string DateOfBirth { get; set; }
    public string PassportNo { get; set; }
    public string PassportExpDate { get; set; }
    public string PassportIssuingCountry { get; set; }
    public string NationalityCountry { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Gender { get; set; }
    public string BirthDate { get; set; }
    public int TotalAmount { get; set; }
    public AdditionalService AdditionalServiceSelect { get; set; }
    public bool additonalservicevisibility2 => (AdditionalServiceSelect == null);
//public bool additonalservicevisibility => ((AdditionalServiceSelect.MealValueLst != null && AdditionalServiceSelect.BaggageValueLst != null) || AdditionalServiceSelect == null);
    public bool additonalservicevisibility1 => (!additonalservicevisibility2);
    public Boolean IsMainPax { get; set; }
    public List<FrequentFlyerDetail> LstFrequentFlyer { get; set; }
 // public List<Airlines> LstFrequentFlyer { get; set; }
    public string FrequentFlyerNo { get; set; }
}

in list view i set passengerdetails that contain 2 count having two value but when i add new value in oassanger details in this passangerdetails it will shiow only 2 data third one not add