How to restrict selection of TreeViewItemAdv when it has child nodes?

<Window.Resources>
        <Style TargetType="{x:Type syncfusion:TreeViewItemAdv}">
            <Style.Triggers>
                <Trigger Property="HasItems" Value="true">
                    <Setter Property="Focusable" Value="false" />
                </Trigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <Grid>
        <syncfusion:TreeViewAdv Name="treeViewAdv"  SelectedItemChanged="TreeViewAdv_SelectedItemChanged" >
            <syncfusion:TreeViewItemAdv Name="treeViewItemAdv" Header="Marital Status">
                <syncfusion:TreeViewItemAdv Header="Single">
                    <syncfusion:TreeViewItemAdv Header="Student"/>
                    <syncfusion:TreeViewItemAdv Header="Exployee"/>
                    <syncfusion:TreeViewItemAdv Header="Businessman"/>
                </syncfusion:TreeViewItemAdv>
                <syncfusion:TreeViewItemAdv Header="Married"/>
                <syncfusion:TreeViewItemAdv Header="Married with Children"/>
            </syncfusion:TreeViewItemAdv>
            <syncfusion:TreeViewItemAdv Header="Baby Vaccines">
                <syncfusion:TreeViewItemAdv Header="Hepatitis B"/>
                <syncfusion:TreeViewItemAdv Header="Tetanus"/>
                <syncfusion:TreeViewItemAdv Header="Polio"/>
                <syncfusion:TreeViewItemAdv Header="Measles"/>
            </syncfusion:TreeViewItemAdv>
            <syncfusion:TreeViewItemAdv Header="Country Information">
                <syncfusion:TreeViewItemAdv Header="Canada"/>
                <syncfusion:TreeViewItemAdv Header="France"/>
                <syncfusion:TreeViewItemAdv Header="Germany"/>
                <syncfusion:TreeViewItemAdv Header="UK"/>
                <syncfusion:TreeViewItemAdv Header="USA"/>
            </syncfusion:TreeViewItemAdv>
        </syncfusion:TreeViewAdv>
    </Grid>