Почему биндинг не хочет работать в данном случае?

<Window x:Class="Сикрет.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Сикрет.Data"
        xmlns:Charting="clr-namespace:ControlLib;assembly=NumericUpDown"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Control.Resources>

        <Style TargetType="MenuItem">
            <Setter Property="FontSize" Value="12"/>
        </Style>

        <Style TargetType="RadioButton">
            <Setter Property="FontSize" Value="11"/>
        </Style>
           
        <DataTemplate x:Key="tplItemRect" DataType="{x:Type local:Item}">
            <Rectangle Width="6" Height="6" Stroke="DeepSkyBlue"/>
        </DataTemplate>

        <ItemsPanelTemplate x:Key="tplHorizontal">
            <StackPanel Visibility="Collapsed"/>
        </ItemsPanelTemplate>

        <HierarchicalDataTemplate DataType="{x:Type local:Item}" ItemsSource="{Binding Items}">
            <StackPanel Orientation="Horizontal">
                <Image Height="14" Margin="0 0 5 4" Source="{Binding PathToImage}"/>
                <TextBlock FontSize="{Binding TreeViewTextSize}" Text="{Binding Title}" Margin="0 0 10 4"/>
                <ItemsControl ItemsSource="{Binding Items}"
                        ItemTemplate="{StaticResource tplItemRect}"
                        ItemsPanel="{StaticResource tplHorizontal}"/>
            </StackPanel>
        </HierarchicalDataTemplate>

        <ContextMenu x:Key="TreeViewContextMenu">
            <MenuItem Header="добавить" Visibility="{Binding TreeViewContextMenuVisibility.Add}"/>
            <MenuItem Header="удалить" Visibility="{Binding TreeViewContextMenuVisibility.Delete}"/>
            <MenuItem Header="переименовать" Visibility="{Binding TreeViewContextMenuVisibility.Rename}"/>
        </ContextMenu>

    </Control.Resources>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="50"/>
            <RowDefinition Height="auto"/>
            <RowDefinition />
        </Grid.RowDefinitions>

        <Grid Grid.Row="0">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="90"/>
                <ColumnDefinition/>
                <ColumnDefinition Width="auto"/>
            </Grid.ColumnDefinitions>
            <Button Content="Открыть" Command="{Binding command_LoadDB}" Grid.Column="0" Height="25" Width="70"/>
            <TextBlock FontSize="11" Text="Размер шрифта:" Grid.Column="2" HorizontalAlignment="Right" Margin="0 15 50 0"/>
            <Charting:NumericUpDown Value="{Binding TreeViewTextSize, Mode=TwoWay}" Grid.Column="2" Height="20" Width="32" VerticalAlignment="Top" HorizontalAlignment="Right" Margin="0 10 10 0" />
        </Grid>

        <Grid Grid.Row="1">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="auto"/>
                <ColumnDefinition/>
                <ColumnDefinition Width="auto"/>
            </Grid.ColumnDefinitions>

            <TextBlock FontSize="12" Text="Фильтр:" Grid.Column="0" Margin="20 4 0 0"/>

            <TextBox Grid.Column="1" Height="20" Margin="10 2 10 10" VerticalAlignment="Top"/>

            <Grid Grid.Column="2">
                <Grid.RowDefinitions>
                    <RowDefinition Height="25"/>
                    <RowDefinition Height="25"/>
                    <RowDefinition Height="25"/>
                </Grid.RowDefinitions>

                <RadioButton IsChecked="True" Content="по названию элемента" Grid.Row="0" Margin="5 5 10 5" Height="15"/>
                <RadioButton Content="по названию раздела" Grid.Row="1" Margin="5 5 10 5" Height="15"></RadioButton>
                <RadioButton Content="по названию файла" Grid.Row="2" Margin="5 5 10 5" Height="15"></RadioButton>
            </Grid>

        </Grid>

        <TreeView Grid.Row="2" Margin="10" ItemsSource="{Binding ItemsTree.Items}" ContextMenu="{StaticResource TreeViewContextMenu}"/>

    </Grid>
</Window>