GroupStyle

            <GridView.GroupStyle>
                <GroupStyle>
                    <GroupStyle.HeaderTemplate>
                        <DataTemplate>
                            <Grid Margin="1,0,0,6">
                                <Button Foreground="{StaticResource ApplicationHeaderForegroundThemeBrush}"
                                    AutomationProperties.Name="Group Title"
                                    Click="Header_Click"
                                    Style="{StaticResource TextBlockButtonStyle}" >
                                        <StackPanel Orientation="Horizontal">
                                            <TextBlock Text="{Binding Title}" Margin="3,-7,10,10" Style="{StaticResource HeaderTextBlockStyle}" TextWrapping="NoWrap" />
                                            <TextBlock Text="{StaticResource ChevronGlyph}" FontFamily="Segoe UI Symbol" Margin="0,-7,0,10" Style="{StaticResource SubheaderTextBlockStyle}" TextWrapping="NoWrap" />
                                        </StackPanel>
                                </Button>
                            </Grid>
                        </DataTemplate>
                    </GroupStyle.HeaderTemplate>
                </GroupStyle>
            </GridView.GroupStyle>