Not save account in second time

[thanhtung6824]

When first time I tried login , it worked well , but second time , when I tried with different account , It not save in database . Here is my code

 app.use(passport.initialize());
     app.use(passport.session());

    passport.serializeUser(function(user, done) {
      done(null, user.id);
    });

    passport.deserializeUser(function(id, done) {
      User.findById(id, function(err, user) {
        done(err, user);
      });
    });

        passport.use(new FacebookStrategy({
            clientID: 'xxx',
            clientSecret: 'xxx',
            callbackURL: "http://localhost:2912/auth/facebook/callback",
             profileFields: ['id', 'name', 'emails']
          },
          function(accessToken, refreshToken, profile, done) {
                User.findOne({'facebook.id':profile.id},function(err,user) {
                    if(err) 
                        return done(err);
                    if(user){
                        return done(null,user);
                    }else{
                        var newUser = new User();
                        newUser.facebook.id = profile.id;
                        newUser.facebook.token = accessToken;
                        newUser.facebook.name  = profile.name.givenName +'' + profile.name.familyName;
                        newUser.facebook.email = profile.emails[0].value;
                        newUser.save(function(err) {
                            if(err)
                                 console.log(err);
                            return done(null,newUser);
                        })
                    }
                });

          }
        ));
app.get('/auth/facebook', passport.authenticate('facebook',{scope:['email']}));

app.get('/auth/facebook/callback', passport.authenticate('facebook', { failureRedirect: '/login' }));

Here is my model

var userSchema = new Schema({

    facebook:{
        id:String,
        token:String,
        email:String,
        name:String
    }
});