WPF Treeview add contextmenu

Question

I am working on a small project which needs to add the treeview items to a listbox, I managed to do this with my treeview:

<HierarchicalDataTemplate DataType="{x:Type data:Category}" ItemsSource="{Binding Path=Products}">
        <TextBlock Text="{Binding Path=CategoryName}" AllowDrop="True"/>
    </HierarchicalDataTemplate>
    <HierarchicalDataTemplate DataType="{x:Type data:Product}" >
        <TextBlock Text="{Binding Path=ModelName}" AllowDrop="True"/>
    </HierarchicalDataTemplate>

And i also tried to add a contextmenu to the treeviewitem like this:

<TreeView x:Name="tv_Project" Margin="5">
                                    <TreeView.ItemContainerStyle>
                                        <Style TargetType="{x:Type TreeViewItem}">
                                            <EventSetter Event="TreeViewItem.PreviewMouseRightButtonDown" Handler="TreeViewItem_PreviewMouseRightButtonDown"/>
                                        </Style>
                                    </TreeView.ItemContainerStyle>
                                    <TreeView.ContextMenu>
                                        <ContextMenu>
                                            <MenuItem Header="Add To Project" Click="MenuItem_OnClick" />
                                        </ContextMenu>
                                    </TreeView.ContextMenu>
                                </TreeView>

The Problem is i just want to add the Eventto my child-node(in my project ModelName) not including parent-node(in my project CategoryName), What should i do?Thanks!

Here is my backend code:

        private void TreeViewItem_PreviewMouseRightButtonDown(object sender, MouseButtonEventArgs e)
    {
        var treeViewItem = VisualUpwardSearch<TreeViewItem>(e.OriginalSource as DependencyObject) as TreeViewItem;
        if (treeViewItem != null)
        {
            treeViewItem.Focus();
            e.Handled = true;
        }
    }

    static DependencyObject VisualUpwardSearch<T>(DependencyObject source)
    {
        while (source != null && source.GetType() != typeof(T))
            source = VisualTreeHelper.GetParent(source);

        return source;
    }
    private void MenuItem_OnClick(object sender, RoutedEventArgs e)
    {
        var item = this.tv_Project.SelectedItem;
        if (item != null)
        {
            lb_Configuration.Items.Add(item);
        }
    }