From the sources
וַיְצַו֙ יְהוָ֣ה אֱלֹהִ֔ים עַל־הָֽאָדָ֖ם לֵאמֹ֑ר מִכֹּ֥ל עֵֽץ־הַגָּ֖ן אָכֹ֥ל תֹּאכֵֽל׃ וּמֵעֵ֗ץ הַדַּ֙עַת֙ ט֣וֹב וָרָ֔ע לֹ֥א תֹאכַ֖ל מִמֶּ֑נּוּ כִּ֗י בְּי֛וֹם אֲכָלְךָ֥ מִמֶּ֖נּוּ מ֥וֹת תָּמֽוּת׃ (ב:טז–ב:יז Bereishit)
And the HaShem commanded the man [Adam HaRishon], saying, “Of every tree of the garden you are free to eat; but as for the tree of knowledge of good and bad, you must not eat of it; for as soon as you eat of it, you shall die.”
Adam HaRishon was allowed to eat from all of the trees in the garden, except for the Tree of Knowledge of Good and Evil. What sort of tree was the Tree of Knowledge of Good and Evil? The Torah leaves the identity of the tree unclear so that people would not come to say that this tree had caused the destruction of the whole world. However, our sages do offer explanations at to what the tree actually was:
-Rabbi Meir says that it was grapes (and therefore possibly refers to wine)
-Rabbi Nechemyah says it was a fig
-Rabbi Yehuda says it was wheat, and Rashi adds that before Adam ate from the tree, wheat grew on trees
-Bereishit Rabba together with Onkelos translates it as an “Etrog”
-Traditionally, it has often been referred to as an “apple”, although this probably mainly because the word “apple” simply meant any “fruit.”
How to Eat it
You could eat any of the above mentioned fruits separately, or try to combine them. For example, use wheat to make a pie crust and make an apple, or apple and fig, pie. Garnish with grapes and candied etrog peel.
I googled and found this delicious-looking Apple and Fig Tart: