Wpf DataGrid RowHeader

I am trying to use a RowHeader in a wpf DataGrid with no luck.

I followed this post

My XAML code

<Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="3*"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <DataGrid Grid.Column="0"  ItemsSource="{Binding Path=Results}" Margin="5">
                <DataGrid.RowHeaderTemplate>
                    <DataTemplate>
                    <TextBlock Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor,  
                                  AncestorType={x:Type DataGridRow}},  
                                  Path=Item.Item1}"/>
                    </DataTemplate>
                </DataGrid.RowHeaderTemplate>
                <DataGrid.Columns>
                <DataGridTextColumn Header="LArmAngle"
                            Binding="{Binding Item2.LArmAngle}" />
                    <DataGridTextColumn Header="PropellerAngle"
                            Binding="{Binding Item2.PropellerAngle}" />
            </DataGrid.Columns>
        </DataGrid>
...
</Grid>

The Results property is specified as follows

public ObservableCollection<Tuple<String, GeometryStateViewModel>> Results
{
    get;
    set;
}

I only see the two columns LArmAngle and PropellerAngle is the resulting DataGrid. I would like to see the following:

            LArmAngle PropellerAngle
aStringHere     1          0.3 
aStringHere     1          0.3 

I was unable to find why I can not display the RowHeader. As a workaround I added an additional column in the data grid to display the sting that I wanted.

...     
<DataGrid Grid.Column="0"  ItemsSource="{Binding Path=Results}" Margin="5">
                <DataGrid.Columns>
                    <DataGridTextColumn Header="Algorithm"
                                Binding="{Binding Item1}" />
                    <DataGridTextColumn Header="LArmAngle"
                                Binding="{Binding Item2.LArmAngle}" />
                    <DataGridTextColumn Header="PropellerAngle"
                                Binding="{Binding Item2.PropellerAngle}" />
                </DataGrid.Columns>
</DataGrid>
...