Simplest monad via C#

IdentityMonad.cs

var z = from x in 5.ToIdentity()
        from y in 6.ToIdentity()
        select x + y;

Console.WriteLine(z);

class Identity<T>
{
    public T Value { get; private set; }
    public Identity(T value) { this.Value = value; }
    public override string ToString()
    {
        return $"[{nameof(Identity<>)}: {nameof(Value)} = {Value}]";
    }
}

static class Ext
{
    public static Identity<T> ToIdentity<T>(this T value)
    {
        return new Identity<T>(value);
    }

    public static Identity<V> SelectMany<T, U, V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T, U, V> s)
    {
        return s(id.Value, k(id.Value).Value).ToIdentity();
    }
}