WPF带小箭头的按钮

<ControlTemplate x:Key="btnTpl" TargetType="RadioButton">
    <StackPanel Orientation="Vertical" Height="30" Background="Transparent">
        <Border Name="border" Background="#006AB8" Height="25">
            <ContentPresenter Name="contentPre" VerticalAlignment="Center" HorizontalAlignment="Center" TextElement.Foreground="#FFF" TextElement.FontSize="12" Margin="0"/>
        </Border>
        <Path x:Name="path" HorizontalAlignment="Center" VerticalAlignment="Center" Data="M 0 0 L 6 4 L 12 0 Z">
            <Path.Fill>
                <SolidColorBrush Color="#006AB8" />
            </Path.Fill>
        </Path>
    </StackPanel>
    <ControlTemplate.Triggers>
        <Trigger Property="IsMouseOver" Value="True">
            <Setter TargetName="border" Property="Margin" Value="2 2 2 0"></Setter>
            <Setter TargetName="border" Property="Height" Value="23"></Setter>
            <Setter Property="TextElement.FontSize" Value="11"></Setter>
        </Trigger>
        <Trigger Property="IsChecked" Value="true">
            <Setter TargetName="border" Property="Border.Background" Value="#15BDF7"></Setter>
            <Setter TargetName="path" Property="Fill" >
                <Setter.Value>
                    <SolidColorBrush Color="#15BDF7" />
                </Setter.Value>
            </Setter>
        </Trigger>
    </ControlTemplate.Triggers>
</ControlTemplate>