That is in fact exactly where it comes from. The Cabala as we have it is Jewish Neoplatonism with a strong Gnostic influence. The Roman writers Celsus and Origen both discussed the Tree of Life, in the 2nd and 3rd centuries respectively -- that is to say, almost a thousand years before it first appeared in Jewish literature, in the school of Rabbi Isaac the Blind in southern France. You can find most of the core themes of later Cabalistic literature even further back, in the writings of the Middle Platonists. That's not to say there's anything wrong with the Jewish Cabala -- it's a brilliant and effective adaptation of Neoplatonism to fit the needs of Jewish mystical spirituality -- but it's an adaptation, not the original source.