Well, I guess you could say that it all depends on your perception of the word "sound." You see, when an object makes a sound, what happens is that air molecules vibrate, and those vibrations reach the inner ear, which is what causes the ear to hear the sound. So, yes, the tree does make a sound because it causes the molecules in the air to vibrate, even if the ear never hears the sound. But, no, the tree doesn't make a hearable sound, because the vibrating molecules never reach the inner ear, so the ear never hears it. That's it in a nutshell. Hope this helps.