Picker MVVM Two Picker has data relative using Binding

I have a model like this ( City.cs in Modle folder)

public class City
    {
        public int Key { get; set; }
        public string Name { get; set; }
        public List<string> Regions { get; set; }
        public City()
        {
            Regions = Regions ?? new List<string>();
        }
    }

Data like this (ViewModel.cs in ViewModel folder)

public List<City> GetCities()
        {
            var c = new List<City>()
            {
                new City() { Key = 1, Name = "Keelung", Regions = { "CenterK", "EastK", "NorthK", "WestK", "SouthK" } },
                new City() { Key = 2, Name = "Hsinchu", Regions = { "HEast", "HNorth", "HCenter" } },
                new City() { Key = 3, Name = "Chiayi", Regions = { "CEast", "CWest" } }
            };
            return  c;
        }

In my view.xaml is

Picker  x:Name="CityPicker"
                             Title= "City"
                             ItemsSource="{Binding CitiesList}"
                              ItemDisplayBinding="{Binding Name}"
                              SelectedItem="{Binding SelectedCity}"/
 Picker  x:Name="RegionPicker" 
                           Title="Region"
                             BindingContext="{x:Reference CityPicker}"
                               ItemsSource="{Binding MyRegion}"
                              ItemDisplayBinding="{Binding Items}"

In my viewmodel.cs is

 public City SelectedCity
{
    get { return _selectedCity; }
    set
    {
        if (_selectedCity != value)
        {
            _selectedCity = value;
            var _myregion = GetCities().Where(x => x.Name == _selectedCity.Name).Select(s => s.Regions);
            OnPropertyChanged();
        }
    }
}
List<string> _myregion;
public List<string> MyRegion
{
    get { return _myregion; }
    set
    {
        if (_myregion != value)
        {
            _myregion = value;
            OnPropertyChanged();
        }
    }
}
public ClinicSearchStartViewModel()
{
    try
    {
        ClinicListResponses = new ObservableRangeCollection<ClinicListResponse>();
        Title = "Search";
        CitiesList = GetCities().OrderBy(k => k.Key).ToList();

        GetClinicListResponsesCommand = new Command<ClinicSearchRequest>(async (clinicsearchrequest)
            => await GetClinicListResponsesAsync(clinicsearchrequest));
    }
    catch (Exception ex)
    {
        throw;
    }
}

How can write a code to make RegionPicker ItemDisplayBinding show CityPicker SelectedItem related Region
for example
CityPicker Select Keelung then click RegionPicker will show { "CenterK", "EastK", "NorthK", "WestK", "SouthK" }

Thanks for Reading````