Xaml and code behind for multilevel binding

<Window x:Class="MultiMedialab.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:MultiMedialab"
        DataContext="{Binding RelativeSource={RelativeSource Self}}"
    Title="MainWindow" Height="350" Width="525"

        Loaded="Window_Loaded">
    <Window.Resources>
        <!-- Book Chapters -->
        <DataTemplate DataType="{x:Type local:BookChapter}">
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding Path=Name}" />
                <ItemsControl ItemsSource="{Binding Path=Pages}" />
            </StackPanel>
        </DataTemplate>

        <!-- Book Pages -->
        <DataTemplate DataType="{x:Type local:BookPage}">
            <StackPanel Orientation="Horizontal" >
                <TextBlock Text="{Binding Path=Id}" Margin="5 0"/>
                <TextBlock Text="{Binding Path=Name}" Margin="5 0"/>
                <ItemsControl ItemsSource="{Binding Path=Exercises}" />
            </StackPanel>
        </DataTemplate>

    </Window.Resources>
    <Grid>
        <ListBox ItemsSource="{Binding Path=Chapters}" Name="lboxTest" />
    </Grid>
</Window>

    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        ObservableCollection<BookChapter> chapterItm = new ObservableCollection<BookChapter>();
        public ObservableCollection<BookChapter> Chapters
        { get { return chapterItm; } }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            List<string> stringcol1 = new List<string>();
            stringcol1.Add("Excercise 1");
            stringcol1.Add("Excercise 2");

            List<string> stringcol2 = new List<string>();
            stringcol2.Add("Excercise 5");
            stringcol2.Add("Excercise 6");

            List<BookPage> subList1 = new List<BookPage>();
            subList1.Add(new BookPage { Name = "Page 1 ", Id = "ID1", Excercises = stringcol1});
            subList1.Add(new BookPage { Name = "Page 2", Id = "ID2", Excercises = stringcol2 });

            List<BookPage> subList2 = new List<BookPage>();
            subList2.Add(new BookPage { Name = "Page 5", Id = "ID 21", Excercises = stringcol1 });
            subList2.Add(new BookPage { Name = "Page 6", Id = "ID22", Excercises = stringcol2 });

            chapterItm.Add(new BookChapter { Name = "Chapter 1", Pages = subList1});
            chapterItm.Add(new BookChapter { Name = "Chapter 2", Pages = subList2 });

        }
    }
    public class BookChapter
    {
        public string Name { get; set; }
        public List<BookPage> Pages { get; set; }
    }
    public class BookPage
    {
        public string Id { get; set; }
        public string Name { get; set; }
        public List<String> Excercises { get; set; }
    }