Question

it is not wise to sleep under a tree why

Answer 1

It is not advised to sleep under a tree at night because at night the trees like us do respiration I.e. take in oxygen and give out carbon dioxide so it may cause lack of oxygen in surroundings.

Answer 2

Tree absorbs only oxygen in night for respiration so it will take all the oxygen we need to breathe, so we would suffocate. So it is not wise to sleep under a tree.