Minecraft wiki entry for Acacia, associated text: The common acacia tree, which has a diagonal trunk and a single canopy.
The multi-canopy acacia, where the trunk forks around the middle of the plant and each end ends in a canopy.
Another form of multi-canopy acacia tree, where a straight trunk is topped with a small canopy, out of which grows additional trunk ending in a second, higher canopy. These trees often grow taller than the common acacia tree.