Wood
Each tree needs its drum measurement done before you can say it's really made of wood.
There are a lot of hoodlums out there that try to dress as trees and confuse people. So make sure you measure their drum before you cut one down or tell someone your secrets under it.
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If you're still not sure if the tree is really made of wood, just take out a small juice (じゅ) box and start drinking it. A wooden tree will show no interest in the juice box at all.
However! A non-wood tree will be really thirsty from pretending to be a wood tree. It will start making sounds and moving and probably say, "Can I have a juice box, please?"