ASP.NET MVC Inserting object and related object into 2 tables

Question

I have two tables: Users and UserOwners. Table UserOwners contains list of users that certain user created (list of child-users) - or to be more precise, it contains UserOwnerID and UserID fields.

So, now I want to create a new user... in Controller I have something like this:

var userOwner = accountRepository.GetUser(User.Identity.Name);
var userOwnerID = userOwner.UserID;

UserReference userReference = new UserReference();
userReference.UserOwnerID = userOwnerID;

if (ModelState.IsValid)
{
    try
    {
        //accountRepository.Add(user);
        //accountRepository.Save();

        return View();
    }
    catch
    {
        return View();
    }
}

What is the easiest way to add new user to a table Users and matching UserOwner to UserOwners table.

Is it suppose to be something like this?

public void Add(User user)
{
     db.Users.InsertOnSubmit(user);
     db.UserReferences.InsertOnSubmit(user.UserReference);
}

public void Save()
{
     db.SubmitChanges();
}

...or I will have to pass two objects and after adding user I must read it's ID and than assign it to userReference object and add that object to DB? If so, how to read ID of the last object added?

Thanks,
Ile