There are two main Doctrines in play; and have been going backwards to the Garden. Trees are symbols of something that is deeply rooted, and can Not change. Immanuel-Christ-Jesus expanded the foundation and taught with power and insight.
Christ's Doctrine was astonishing[Matt.7:28]. He gave clear instructions on the Kingdom of Heaven; and He exposed the Hypocrites. Religion is one thing: but to copy the Levi-Priesthood and turn people to Religion is another matter. Not only were the Fakes exposed, but we received a strong admonishment to be on the lookout for small fragments of their-Doctrine.
Following Immanuel leads to Life. Following the Tree of Knowledge leads to Death: because Satan is Death. Matt.16:12 appears to be about bread and feeding thousands of people with a few loaves of bread: It is a caution of the leaven[small] of the "Doctrine of the Pharisees and the Sadducee's."
Immanuel-Christ-Jesus Doctrine is Liberty, and Life. Religion is bondage. Throughout the Gospels we see the Doctrine of Cain being followed by the Religious one's. They plotted and schemed for 3-1/2 yrs. on murdering Christ: the same Doctrine exist today through the Children of Darkness[Tares] and their miss-educated followers.
Prov.4:2 "For I give you good Doctrine: forsake not my Law." The Hypocrites[Fakes, Religious ones] "are altogether brutish and foolish: the stock[idols] is a Doctrine of vanities." Reasonable people given a choice between LIFE and Death would overwhelmingly choose LIFE: if only they could see the Truth!