Cascading Dropdown & Multiselect Option in ListBox Using WPF

<Window x:Class="CascadingDropDown.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="203" Width="656" Loaded="Window_Loaded">
    <Grid>
        <GroupBox Header="SimpleCascadingDropdown" Margin="12,12,0,0" Name="grpCascadingDropdown" Height="147" VerticalAlignment="Top" HorizontalAlignment="Left" Width="239">
            <Grid Height="101" Width="224">
                <Grid.RowDefinitions>
                    <RowDefinition Height="53*" />
                    <RowDefinition Height="52*" />
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="8*" />
                    <ColumnDefinition Width="235*" />
                </Grid.ColumnDefinitions>
                
                
                <Label HorizontalAlignment="Left" Margin="6,6,0,23" Name="lblCountry" Width="59" Grid.ColumnSpan="2">Country</Label>
                <ComboBox Margin="54,7,49,23" Name="cmbCountry" ItemsSource="{Binding SingleCountryList}" DisplayMemberPath="CountryName" IsSynchronizedWithCurrentItem="True" SelectionChanged="cmbCountry_SelectionChanged" Grid.Column="1" />
              
                <Label Margin="7,36,0,41" Name="lblState" HorizontalAlignment="Left" Width="50" Grid.Column="1" Grid.RowSpan="2">State</Label>
                <ComboBox Margin="54,38.5,49,43.5" Name="cmbState" ItemsSource="{Binding SingleStateList}" DisplayMemberPath="StateName" IsSynchronizedWithCurrentItem="True" SelectionChanged="cmbState_SelectionChanged" Grid.Column="1" Grid.RowSpan="2" />
                <Label Margin="7,11,0,13" Name="lblCity" HorizontalAlignment="Left" Width="31" Grid.Column="1" Grid.Row="1">City</Label>
                <ComboBox Margin="56,16,49,13" Name="cmbCity" ItemsSource="{Binding SingleCityList}" DisplayMemberPath="CityName" IsSynchronizedWithCurrentItem="True" Grid.Column="1" Grid.Row="1" />
            </Grid>
        </GroupBox>
        
        
        <GroupBox Header="SimpleCascadingListbox" Margin="291,12,79,0" Name="grpCascadingListbox" Height="147" VerticalAlignment="Top">
            <Grid Height="209">
                <Label Height="28" Margin="6,12,0,0" Name="lblNewCountry" VerticalAlignment="Top" HorizontalAlignment="Left" Width="51">Country</Label>
                <ListBox Margin="60,14,52,0" Name="lstCountry" Height="26" VerticalAlignment="Top" ItemsSource="{Binding MultipleCountryList}" DisplayMemberPath="CountryName" SelectionMode="Multiple" IsSynchronizedWithCurrentItem="True" SelectionChanged="lstCountry_SelectionChanged"/>
                <Label Margin="10,46,0,0" Name="lblNewState" HorizontalAlignment="Left" Width="43" Height="24.862" VerticalAlignment="Top">State</Label>
                <ListBox Margin="59,46,55,0" Name="lstState" Height="27.362" VerticalAlignment="Top" SelectionMode="Multiple" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding MultipleStateList}" DisplayMemberPath="StateName" SelectionChanged="lstState_SelectionChanged"/>
                <Label Margin="7,86.361,0,96.362" Name="lblNewCity" HorizontalAlignment="Left" Width="46">City</Label>
                <ListBox Margin="59,88.723,55,96.362" Name="lstCity" SelectionMode="Multiple" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding MultipleCityList}" DisplayMemberPath="CityName"/>
            </Grid>
        </GroupBox>
    </Grid>
</Window>