[XmlRoot("root")]
    public class MyClass1 {
        [XmlElement("MyClass")]
        public List<MyClass> A { get; set; }
    }

    public class MyClass {
        public string B { get; set; }
    }


    class Program {
        static void Main(string[] args) {
            MyClass1 root = new MyClass1();
            root.A = new List<MyClass>(new MyClass[] { new MyClass { B = "string1" }, new MyClass { B = "string2" } });

            using(MemoryStream ms = new MemoryStream()) {
                XmlSerializer serializer = new XmlSerializer(typeof(MyClass1));
                serializer.Serialize(ms, root);

                ms.Seek(0, SeekOrigin.Begin);
               Console.WriteLine(Encoding.Default.GetString(ms.ToArray()));                
            }

            Console.Read();
        }
    }