WPF TreeView中节点之间的行

<TreeView>
    <TreeView.ItemContainerStyle>
       <Style TargetType="{x:Type TreeViewItem}">
           <Setter Property="Template">
               <Setter.Value>
                   <ControlTemplate TargetType="{x:Type TreeViewItem}">
                        <Grid>
                            <Grid.ColumnDefinitions>
                               <ColumnDefinition MinWidth="19" Width="Auto"/>
                               <ColumnDefinition Width="Auto"/>
                               <ColumnDefinition Width="*"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition Height="Auto"/>
                            </Grid.RowDefinitions>
                           <ToggleButton x:Name="Expander" ClickMode="Press" IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" Style="{StaticResource ExpandCollapseToggleStyle}"/>
                           <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="1" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="true">
                               <ContentPresenter x:Name="PART_Header" ContentSource="Header" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </Border>
                           <ItemsPresenter x:Name="ItemsHost" Grid.ColumnSpan="2" Grid.Column="1" Grid.Row="1"/>
                            <Line Grid.ColumnSpan="2" Stroke="Black" X1="0" X2="1" VerticalAlignment="Center" HorizontalAlignment="Left" Margin="19,0,0,0"/>
                        </Grid>
                       <ControlTemplate.Triggers>
                           <Trigger Property="IsExpanded" Value="false">
                               <Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
                            </Trigger>
                           <Trigger Property="HasItems" Value="false">
                               <Setter Property="Visibility" TargetName="Expander" Value="Hidden"/>
                            </Trigger>
                           <MultiTrigger>
                               <MultiTrigger.Conditions>
                                   <Condition Property="HasHeader" Value="false"/>
                                   <Condition Property="Width" Value="Auto"/>
                                </MultiTrigger.Conditions>
                               <Setter Property="Margin" Value="0,0,0,0"/>
                               <Setter Property="Padding" Value="0,0,0,0"/>
                               <Setter Property="MinHeight" Value="0"/>
                            </MultiTrigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </TreeView.ItemContainerStyle>
</TreeView>