WPF树视图，使用多个数据源进行层次数据绑定

I have this wpf structure:

我有这个wpf结构：

 <TreeView x:Name="tree" ItemsSource="{Binding MainDirectory}"> 
                <TreeView.ItemTemplate>
                    <HierarchicalDataTemplate ItemsSource="{Binding _directory}">
                        <TreeViewItem Header="{Binding _name}" >
                        </TreeViewItem>
                    </HierarchicalDataTemplate>
                </TreeView.ItemTemplate>

 </TreeView>
 <Tre