+---------+------+-----+
| Country | Name | Age |
+---------+------+-----+
|         | Lisa | 24  |
+         +------+-----+
| Danmark |  Per | 32  |
+         +------+-----+
|         | Hans | 33  |
+---------+------+-----+
| Germany | Mick | 22  |
+---------+------+-----+

<Window.Resources>
        <CollectionViewSource x:Key="CvsKey">
            <CollectionViewSource.GroupDescriptions>
                <PropertyGroupDescription PropertyName="Country"/>
            </CollectionViewSource.GroupDescriptions>
        </CollectionViewSource>
    </Window.Resources>

    <Grid>
        <DataGrid x:Name="dg" Loaded="dg_Loaded" HorizontalScrollBarVisibility="Disabled" HeadersVisibility="All" Grid.Column="0" RowHeaderWidth="0" CanUserAddRows="False" AutoGenerateColumns="False"  VerticalContentAlignment="Center" HorizontalContentAlignment="Center">
            <DataGrid.Columns>
                <DataGridTemplateColumn Header="Country"  Width="75">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Grid>
                                <TextBlock VerticalAlignment="Center" Text="{Binding Name}"/>
                            </Grid>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTemplateColumn Header="Name"  Width="75">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <DataGrid ItemsSource="{Binding Items}" IsReadOnly="True" AutoGenerateColumns="False" HeadersVisibility="None">
                                <DataGrid.Columns>
                                    <DataGridTemplateColumn Width="*">
                                        <DataGridTemplateColumn.CellTemplate>
                                            <DataTemplate>
                                                <TextBlock Text="{Binding Name}"/>
                                            </DataTemplate>
                                        </DataGridTemplateColumn.CellTemplate>
                                    </DataGridTemplateColumn>
                                </DataGrid.Columns>
                            </DataGrid>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
          </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

private void dg_Loaded(object sender, RoutedEventArgs e)
    {
        var groups = (this.Resources["CvsKey"] as CollectionViewSource).View.Groups;
        dg.ItemsSource = groups;
    }