Matthew 7:16-18 tells us:
“Do men gather grapes from thorn bushes or figs from thistles? Even so, every good tree bears good fruit, but a bad tree bears bad fruit. A GOOD TREE CANNOT BEAR BAD FRUIT, NOR CAN A BAD TREE BEAR GOOD FRUIT.”
A fruit is always the result of the tree that is behind it. No fruit can be produced without a tree, and no fruit can be different than the tree that produced it. The Lord uses this figure here to tell us that what a man brings forth is the result and in direct analogy with the treasure he has in his heart. A good treasure produces good fruit, and an evil treasure produces evil fruit.