WPF MaterailDesign TreeView节点默认全部展开

加载TreeView后默认节点全部折叠； 

<TreeView  x:Name="treeView"   Grid.Row="0"  Foreground="White"   ItemsSource="{Binding NavMenus}"    MinWidth="220">
            <TreeView.Resources>
                <HierarchicalDataTemplate DataType="{x:Type domain:NavMenuModel}"   ItemsSource="{Binding ChildMenus}">
                    <TextBlock Text="{Binding MenuName}" Margin="3 2" />
                </HierarchicalDataTemplate>
                <DataTemplate DataType="{x:Type domain:MenuModel}">
                    <TextBlock  Text="{Binding MenuName}"  Margin="3 2"/>
                </DataTemplate>              
            </TreeView.Resources>
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="SelectedItemChanged">
                    <i:InvokeCommandAction Command="{Binding SelectItemChangeCommand}" CommandParameter="{Binding ElementName=treeView,Path=SelectedItem}"/>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </TreeView>       

如果写上

 <TreeView.ItemContainerStyle>
                        <Style TargetType="{x:Type TreeViewItem}">
                            <Setter Property="IsExpanded" Value="{Binding IsExpanded,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"/>
                            <Setter Property="IsSelected" Value="{Binding IsSelected,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"/>
                        </Style>
                    </TreeView.ItemContainerStyle>

则MaterialDesign 的样式失效了，如何解决这个问题呢?

想到了样式的“继承”:

 <UserControl.Resources>
        <Style TargetType="TreeViewItem" BasedOn="{StaticResource MaterialDesignTreeViewItem}">
            <Setter Property="IsExpanded" Value="{Binding IsExpanded,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"/>
            <Setter Property="IsSelected" Value="{Binding IsSelected,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"/>
        </Style>
    </UserControl.Resources>