ComboBox in DataGrid binding

Question

Hi, I have datagrid and I bound some data to each row (ObservableCollection<Contact>) Name, Surname, Group, Address are in Contact object as property. For group column I want to add comboBox, where is some Group Collection

namespace BusinessLayer.Structure
{
    public class GroupList : ObservableCollection<Group>
    {
        public GroupList()
        {
            Manager.PrepareData _groups = new Manager.PrepareData(); // get ObservableCollection<Group>
            foreach(Group group in _groups.LoadGroups())
            {
                this.Add(group);
            }
        }
    }
}


namespace BusinessLayer.Structure
{
    public class Group
    {
        public Guid ID_Group { get; set; }
        public string Name_Group { get; set; }
    }
}

namespace BusinessLayer.Structure
{
    public class Contact
    {
        public Guid  Id { get; set; };
        public string Name { get; set; };
        public string Surname { get; set; };
        public string Group { get; set; };
        public string Address { get; set; };
    }
}

How can I bind data in DataGrid in XAML? DataGrid is in PresentationLayer namespace.

                    <DataGridTemplateColumn.CellEditingTemplate>
                        <DataTemplate>
                            <ComboBox x:Name="group_combobox" SelectedValuePath="Name_Group"
                                      SelectedValue="{Binding Group}"
                                      DisplayMemberPath="Name"
                                      ItemsSource="{Binding Path=DataContext.GroupList,
                                        RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}"
                                      IsReadOnly="True" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellEditingTemplate>

I tried a lot of ideas but no solution. Could someone help me, please? Thanks