如何更改HierarchicalDataTemplate？

Question

如何在我的TreeView中更改HierarchicalDataTemplate by DataTrigger？

<TreeView Grid.Row="2" Grid.Column="1" Grid.ColumnSpan="2"
          ItemsSource="{Binding Nodes}">
    <TreeView.ItemContainerStyle>
        <Style TargetType="TreeViewItem">
            <Setter Property="IsExpanded" Value="True" />
        </Style>
    </TreeView.ItemContainerStyle>
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate ItemsSource="{Binding Nodes}">
            <HierarchicalDataTemplate.Triggers>
                <DataTrigger Binding="{Binding Type}" Value="group">
                    <Setter Property="Content">
                        <Setter.Value>
                            <TextBlock Text="{Binding Title}" />
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding Type}" Value="page">
                    <Setter Property="Content">
                        <Setter.Value>
                            <StackPanel Orientation="Horizontal">
                                <TextBlock Text="{Binding Page.Name}" />
                                <TextBlock Text="{Binding Page.Format}" />
                            </StackPanel>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
            </HierarchicalDataTemplate.Triggers>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

在TreeView的ItemSource中，我放置了节点对象的列表：

public class Node
{
    public string Title { get; set; }
    public Page Page { get; set; }
    public string Type { get; set; }
    public List<Node> Nodes { get; set; } = new List<Node>();
}

这就是结果：

​

​

我做错了什么？