Добавить элемент в TitleBar окна

<Window x:Class="lol.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d">
 
    <Window.Style>
        <Style TargetType="{x:Type Window}">
            <Setter Property="WindowChrome.WindowChrome">
                <Setter.Value>
                    <WindowChrome/>
                </Setter.Value>
            </Setter>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Window}">
                        <Button Name="btnHelp" Height="25" HorizontalAlignment="Right" Margin="0,0,120,0" VerticalAlignment="Top" Width="40" WindowChrome.IsHitTestVisibleInChrome="True">?</Button>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Style>
 
    <Grid Background="Green">
        <TextBlock VerticalAlignment="Center" HorizontalAlignment="Center">Контент</TextBlock>
    </Grid>
</Window>