Try this code..
var results = from p in persons
group p.car by p.PersonId into g
select new { PersonID = g.Key, Cars = g.ToList() };
or incase of chain statement..
var results = persons.GroupBy(p => p.PersonId, p => p.car,
(key, g) => new { PersonId = key, Cars = g.ToList() });
If this solves your issue kindly up vote and mark this as solution.. Thanks..