Usual explanation in all books relating to Jambūdīpa is rose apple tree as enumerated below:
Jambūdīpa : the auspicious Great Island where the Rose Apple (Jambu) tree grows. It is one of the Four Great Island – continents, that constitute the world system, the three others being : Uttarakuru, the Northern Island, Pubbavideha, the Eastern Island and Aparagoyana, the Western Island.