Apple trees generate in the following biomes:
Plains, Sunflower Plains, Birch Forest, Birch Forest Hills, Forest, Forest Hills.
Standard: 5,000 per 1,000,000 chunks in groups of 1 to 3
Large: 2,500 per 1,000,000 chunks
Apple trees are made of apple tree leaves which when broken have a chance to drop apples and apple tree saplings. The logs are oak logs.
Apple Trees can be planted by placing an apple tree sapling on grass or dirt. The sapling can also be bonemealed to help it grow faster.