public class AggregateRepository
  {
    // IRL this should be a data store of sorts
    private static Dictionary<Guid, List<Event>> eventStore = new Dictionary<Guid, List<Event>>();

    public void Save(Aggregate aggregate)
    {
      if (!eventStore.ContainsKey(aggregate.Id))
        eventStore[aggregate.Id] = new List<Event>();
      eventStore[aggregate.Id].AddRange(aggregate.NewEvents); // OK, a bit more involved IRL
    }
  }