Biomes O' Plenty Wiki

Apple trees could be found in the orchard biome and were a source of apples.

There are four types of apple leaves: leaves, leaves with flowers, leaves with green fruit, and leaves with red fruit. Only the last one, the red fruit, will drop apples when broken. You can also harvest apples by right-clicking the leaves with red fruits.

Apple Trees were apparently removed due to concerns that they made finding apples too easy.