tree rewards=bug level different hammer color=diffrent bugs so try to experimnet, though i use the gold one most
to get major rewards, wait for the flash/charge of the hammer and wait for it to reach the end of the hammer, or when it ends a la R button hammer charge, then press X at the exact time.
you will know you got it perfect if the player raises his/her foot before hitting the tree. also, if your player seems tired after hitting tree (bend down exhausted like), it means fail. few rewards there.
begin with white hammer, its easier to time