Gérer combobox différente d'un grid

<Window x:Class="WpfApplicationGrid.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfApplicationGrid"  
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:viewmodel/>
    </Window.DataContext>
    <Window.Resources>
        <!-- CollectionViewSourceで参照出来るようにしておいて -->
        <CollectionViewSource   x:Key="ListSource"   Source="{Binding Path=Employees.lalist}" />
        <CollectionViewSource   x:Key="ResultatSource"   Source="{Binding resultat}" />

        <!--<DataTemplate x:Key="EmpTemplate" DataType="{x:Type local:Employee}">
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding resultat}"></TextBlock>                
            </StackPanel>
        </DataTemplate>-->
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="32"></RowDefinition>
        </Grid.RowDefinitions>
        <Grid Grid.Row="0">
            <DataGrid AutoGenerateColumns="False" Name="myGrid" Margin="10" ItemsSource="{Binding Employees}" SelectionChanged="myGrid_SelectionChanged">
                <DataGrid.Columns>
                    <DataGridTextColumn Header="Name"  Binding="{Binding Path=Name}" />
                    <DataGridComboBoxColumn x:Name="truccombo" Header = "Party" SelectedItemBinding = "{Binding Path=resultat}"                   
                                            DisplayMemberPath="Name" 
                                            />
                    <DataGridTextColumn Header="RName"  Binding="{Binding Assign,Mode=OneWay}"  />


                </DataGrid.Columns>
            </DataGrid>
        </Grid>
        <Grid Grid.Row="1">
            <Button Content="Button" HorizontalAlignment="Left" Height="12" Margin="138,10,0,0" VerticalAlignment="Top" Width="91" Click="Button_Click"/>

        </Grid>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplicationGrid
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void myGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (e.AddedItems.Count > 0)
            {
                object o = e.AddedItems[0];
                Employee ee = o as Employee;
                if (ee != null)
                {
                    truccombo.ItemsSource = ee.lalist;
                }
            }
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            int i = 4;
            e = e;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WpfApplicationGrid
{
    public class Lttt
    {
        private string _name;
        public string Name
        {
            get
            {
                return _name;
            }
            set
            {
                _name = value;
            }

        }
        public Lttt(string s)
        {
            _name = s;
        }
    }
    public class Employee : INotifyPropertyChanged
    {

        public event PropertyChangedEventHandler PropertyChanged;
        ObservableCollection<Lttt> _lista;
       /* public static ObservableCollection<string> _Genders;
        public ObservableCollection<string> Genders
        {
            get
            {
                return _Genders;
            }
            set
            {
                _Genders = value;
            }
        }*/
        private Lttt _resultat;
        public Lttt resultat
        {
            get
            {
                return _resultat;
            }
            set
            {
                _resultat = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs("Assign"));
                }
            }
        }
        public string Name { get; set; }
        public string Assign {
            get
            {
                string sd = "";
                if (_resultat!=null)
                    sd = _resultat.Name;
                return sd;
            }
       }
        public ObservableCollection<Lttt> lalist
        {
            get
            {
                return _lista;
            }

        }

        public Employee(string _sn, ObservableCollection<Lttt> maliste)
        {
            Name = _sn;
            //Gender = _sg;
            _resultat = null;
            _lista = maliste;


        }
    }
    public class viewmodel
    {
        //private Lttt _resultat;
        public static ObservableCollection<Employee> Employees { get; set; }


        public viewmodel()
        {


            ObservableCollection<Lttt> _lista,_listb;

            _lista = new ObservableCollection<Lttt>();
            _lista.Add(new Lttt("1"));
            _lista.Add(new Lttt("2"));
            _lista.Add(new Lttt("3"));
            _listb = new ObservableCollection<Lttt>();
            _listb.Add(new Lttt("4"));
            _listb.Add(new Lttt("5"));
            _listb.Add(new Lttt("6"));
            Employees = new ObservableCollection<Employee>()
            {
                new Employee("ABCgroup1",_lista),
                new Employee("CDEFgroup1",_lista),
                new Employee("UVDgroup2",_listb),
                new Employee("XYZgroup2",_listb),
            };

            //myGrid.ItemsSource = Employees;
            //Gender.ItemsSource = Genders;
        }        
    }
}