WPF user control cannot be seen in inspect

Here is a question that I already has an answer. I want to mark here to help others. I have a self-defined tabcontrol. When I do the automation, the control tree of tabitem doesn't populated in inspect. Here is the code:

    <Window.Resources>
        <Style x:Key="TabControlStyle1" TargetType="{x:Type TabControl}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TabControl}">
                        <Grid x:Name="templateRoot" ClipToBounds="true" SnapsToDevicePixels="true" KeyboardNavigation.TabNavigation="Local">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition x:Name="ColumnDefinition0"/>
                                <ColumnDefinition x:Name="ColumnDefinition1" Width="0"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition x:Name="RowDefinition0" Height="Auto"/>
                                <RowDefinition x:Name="RowDefinition1" Height="*"/>
                            </Grid.RowDefinitions>
                            <TabPanel x:Name="headerPanel" Background="Transparent" Grid.Column="0" IsItemsHost="true" Margin="2,2,2,0" Grid.Row="0" KeyboardNavigation.TabIndex="1" Panel.ZIndex="1"/>
                            <Border x:Name="contentPanel" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="0" KeyboardNavigation.DirectionalNavigation="Contained" Grid.Row="1" KeyboardNavigation.TabIndex="2" KeyboardNavigation.TabNavigation="Local">
                                <ContentPresenter ContentSource="SelectedContent" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </Border>
                        </Grid>

                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
    <Grid>
        <TabControl Margin="5" Style="{DynamicResource TabControlStyle1}">
            <TabItem Header="tab 1">
                <Button Width="90" Height="90" Content="btn1"/>
            </TabItem>
            <TabItem Header="tab 2">
                <Button Width="90" Height="90" Content="btn2"/>
            </TabItem>
        </TabControl>
    </Grid>

Why the Tabitem is unseen in inspect?

I has to add the x:Name to ContentPresenter. And x:Name must be PART_SelectedContentHost

<ContentPresenter x:Name="PART_SelectedContentHost" ContentSource="SelectedContent" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>