Dilemma might be a better choice for what the fruit is called that holds the oxymoron seed.

Dilemma means a situation in which a difficult choice has to be made between two or more alternatives, especially equally undesirable ones.

A seed of oxymoron, good-evil, or evil-good. How does it taste, does it taste "good" or would the oxymoron taste bad (evil).

Consider the oxymoron Bitter-sweet, is it good taste, or bad?

To elaborate a little more: if you take an oxymoron seed: good-evil, and you grow that seed into a tree, you would get another tree of knowledge of good and evil.

It wasn't apples. The tree was the tree "of knowledge of good and evil".

If a tree is knowledge of good and evil, what do trees do to reproduce? They have fruit. That is the seed of knowledge of both good and evil? An oxymoron. A conflation of good and evil.

So, the fruit of the tree of knowledge of good and evil would be an oxymoron of such, good evil, or evil good.