Check if tree branch has data

I have a menu tree in a mysql database which I can display easily by a recursive php function

INSERT INTO `car_nav` (`rowid`,`parent`,`name`) VALUES
(1,NULL,'cars'),
(2,1,'BMW'),
(3,1,'VW'),
(4,1,'Audi'),
(5,2,'4WD'),
(6,4,'coupe'),
(7,3,'coupe'),
(8,7,'4WD'),
(9,3,'limousine'),
etc...

INSERT INTO `car_data` (`navid`,`details`) VALUES
(5,'this car has...'),
(5,'a luxury model for...'),
(6,'another car for...'),
etc...

Is there a way in PHP to show only the branches who end in an entry from the car_data DB and leave out those who are blind?
In above example all branches that origin from VW would be hidden, as there are no models assigned.