C# WPF How to bind a nested class to nested datagrid

Question

in WPF, How to bind data from nested classs to a nested datagrid? Why nested datagrid unable to read the class? what error i am doing?

public class Student
{
      public int Id { get; set; }
      public string Name { get; set; }
      public DateTime Birthday { get; set; }
      public Marks myMarks { get; set; }
}

public class Marks
{
      public double English { get; set; }
      public double Maths { get; set; }
      public double Science { get; set; }
}

itemsource for main-datagrid

private void Page_Loaded(object sender, RoutedEventArgs e)
{
   List<Student> myStudents = new List<Student>();

    Marks JohnMark = new Marks();
    JohnMark.English = 75;
    JohnMark.Maths = 85;
    JohnMark.Science = 95;

    Marks RichardMark = new Marks();
    RichardMark.English = 70;
    RichardMark.Maths = 80;
    RichardMark.Science = 90;

    Marks SamMark = new Marks();
    SamMark.English = 72;
    SamMark.Maths = 82;
    SamMark.Science = 92;

    myStudents.Add(new Student() { Id = 1, Name = "John Doe", Birthday = new DateTime(1971, 7, 23), myMarks = JohnMark });
    myStudents.Add(new Student() { Id = 2, Name = "Richard Doe", Birthday = new DateTime(1974, 1, 17), myMarks = RichardMark });
    myStudents.Add(new Student() { Id = 3, Name = "Sammy Doe", Birthday = new DateTime(1991, 9, 2), myMarks = SamMark });

    DG_myStudents.ItemsSource = myStudents;
}

and below is my XAML code, Am i doing any error in class structure? Please help me.

<DataGrid x:Name="DG_myStudents" RowDetailsVisibilityMode="Visible">
        <DataGrid.RowDetailsTemplate>
            <DataTemplate>
                <DataGrid x:Name="DG_myMarks" ItemsSource="{Binding myMarks}" />
            </DataTemplate>
        </DataGrid.RowDetailsTemplate>
</DataGrid>

Nothing, the nested datagrid "DG_myMarks" is not showing any data. And when i bind "myMarks" to a label to just to see any thing happening there, then label is showing "Marks class name" like this "MyNameSpace.myPage+Marks"