<GroupBox Margin="5">

            <StackPanel>

                <RadioButton IsChecked="true">1</RadioButton>

                <RadioButton>2</RadioButton>

                <RadioButton>3</RadioButton>

            </StackPanel>

        </GroupBox>

        <RadioButton GroupName="1">11</RadioButton>

        <RadioButton GroupName="1">12</RadioButton>

        <RadioButton GroupName="2">13</RadioButton>