connect ComboBox to a list in WPF datagrid

List users = new List();
users.Add(new User() { Id = 1, Name = "John Doe", Birthday = new DateTime(1971, 7, 23), ImageUrl = "http://www.wpf-tutorial.com/images/misc/john_doe.jpg" });
users.Add(new User() { Id = 2, Name = "Jane Doe", Birthday = new DateTime(1974, 1, 17) });
users.Add(new User() { Id = 3, Name = "Sammy Doe", Birthday = new DateTime(1991, 9, 2) });

dgUsers.ItemsSource = users;

}

public class User
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime Birthday { get; set; }
public string ImageUrl { get; set; }
public string Details
{
get
{
return String.Format("{0} was born on {1} and this is a long description of the person.", this.Name, this.Birthday.ToLongDateString());
}
}
}

public class ProductType : List
{
public ProductType()
{
this.Add("TA0300-01");
this.Add("TA0302-01");
this.Add("TA0303-01");
this.Add("TA0302-02");
}
}

}