TreeMenuItem.xaml

<UserControl
    x:Class="MyApplication.TreeMenuItem"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:MyApplication"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="40"
    d:DesignWidth="250" Margin="0" Padding="0" Height="40" SizeChanged="customMenuItem_SizeChanged"
             >
    <UserControl.Resources>
        <x:String x:Key="ChevronGlyph">&#xE26B;</x:String>
        <!--
            Collection of grouped items displayed by this page, bound to a subset
            of the complete item list because items in groups cannot be virtualized
        -->
    </UserControl.Resources>

    <StackPanel x:Name="menuPanel" Orientation="Horizontal" HorizontalAlignment="Left" Width="250" Margin="0" Background="Transparent" VerticalAlignment="Center">
        <StackPanel Orientation="Horizontal" HorizontalAlignment="Left" Width="210" Margin="0" Background="Transparent">
            <FontIcon x:Name="menuIconFontIcon" Glyph="&#xE1D3;" Margin="8,0,0,0" VerticalAlignment="Center" FontSize="24"/>
            <TextBlock x:Name="textBlock" Margin="10,0,0,0" Text="Text" VerticalAlignment="Center" FontSize="32" />
        </StackPanel>
        <StackPanel Width="40">
            <Button x:Name="expandButton" Style="{StaticResource LeftMenuButtonStyle}" Width="40" VerticalContentAlignment="Center" Canvas.Left="210" Click="expandButton_Click">
                <FontIcon x:Name="expandButtonFontIcon" Glyph="&#xE09D;" FontSize="24" Margin="0" VerticalAlignment="Center"/>
            </Button>
        </StackPanel>
    </StackPanel>
</UserControl>