It's found that the ic2 chansaw is not able to cut down trees which is big enough(for example, jungle trees). I guess it is caused by the durability check because the ic2 chainsaw only have 27 durability even though it can be used for a long time(when you cut down the trees using ic chainsaw, it doesn't consume durability directly,instead, it consumes EU). As a result, I think, the tree chopper consider the chainsaw not durable enough to cut down big trees.