Метод расширения Человек на помощь!
/// <summary>
/// Adds all given items to the collection
/// </summary>
/// <param name="collection">The collection.</param>
/// <param name="toAdd">Objects to add.</param>
public static void AddAll<T>(this IList<T> collection, params T[] toAdd)
{
foreach (var o in toAdd)
collection.Add(o);
}