The Tree class is set to be used by various blocks for setting the TreeSpecies in the MaterialData, however it doesn't set it correctly for block types. The WoodenStep class also has this issue. They make the assumption that only the first two bits are used for TreeSpecies when for WOOD, SAPLING, WOOD_STEP, WOOD_DOUBLE_STEP the values 0-5 are used (first three bits). Also LEAVES_2 and LOG_2 uses the first bit to represent ACACIA or DARK_OAK, which has not yet been implemented.