You don’t get bad fruit from a good tree. You don’t get good fruit from a bad tree.
Every tree bears a specific kind of fruit. You don’t get figs from thorns. You don’t get grapes from briars.
Here’s another koan.
It may be tempting to use it as a measure for assessing the good and bad in others, and to try to figure out what kind of “tree” they are.
Avoid this. The koan is not about anyone else. It’s to help you figure out what kind of tree you are.