How to get access to gruop style element in datagrid.

Question

 I have implement datagrid as below and i have no idea how to with checkbox named SelectGroupCheckBox check all checkbox in gruop.

 

<DataGrid x:Name="PersonDataGrid"
                  HorizontalAlignment="Left"
                  VerticalAlignment="Top"
                  Height="450" Width="902"
                  CanUserAddRows="False"
                  AutoGenerateColumns="False" >
            <DataGrid.GroupStyle>
                <GroupStyle>
                    <GroupStyle.ContainerStyle>
                        <Style TargetType="{x:Type GroupItem}">
                            <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate TargetType="{x:Type GroupItem}">
                                        <Expander IsExpanded="False">
                                            <Expander.Header>
                                                <StackPanel Orientation="Horizontal">
                                                    <CheckBox x:Name="SelectGroupCheckBox" >

                                                    </CheckBox>
                                                    <TextBlock Text="{Binding Name}"/>
                                                </StackPanel>
                                            </Expander.Header>
                                            <Expander.Content>
                                                <ItemsPresenter/>
                                            </Expander.Content>
                                        </Expander>
                                    </ControlTemplate>
                                </Setter.Value>
                            </Setter>
                        </Style>
                    </GroupStyle.ContainerStyle>
                </GroupStyle>
            </DataGrid.GroupStyle>
            <DataGrid.Columns>
                <DataGridTemplateColumn>
                    <DataGridTemplateColumn.Header>
                        <CheckBox Content="Select All"
                                  Checked="CheckBox_Checked"
                                  Unchecked="CheckBox_Unchecked"/>
                    </DataGridTemplateColumn.Header>
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <CheckBox IsChecked="{Binding IsSelected,
                                                  Mode=TwoWay,
                                                  UpdateSourceTrigger=PropertyChanged}"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTextColumn Binding="{Binding Person.Name}"
                                    Header="Name"
                                    Width="120"
                                    IsReadOnly="True"/>
            </DataGrid.Columns>
        </DataGrid>