Minecraft wiki entry for Oak, associated text: A giant oak tree generated at the wrong biome.
An oak tree that generated over a lava pit. The dirt under it was replaced by stone.
An unsupported oak tree.
A tree generated next to a lava lake, which caught on fire.
A fallen oak with some logs in midair.
A fallen oak where most of the logs are lower than the base.
An oak with two different leaf colors.
A fallen oak where most of the logs are floating directly above a river.