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>