Question

because of rain trees are there or because of trees rain falls

Answer 1

It can be said that trees are the primary causes of rain. When tree absorb water, some water is evaporated due to hot weather and some water evaporates due to transpiration. This water evaporates and form clouds which when saturated pours down as rain.As water can come from many sources including rain but not necessarily from rains, so that makes trees the primary source of rainfall.

Answer 2

actually both are true.
Rain gives water to trees helping them grow
and trees do transpiration (evaporation of water from leaves) to help in rain
Hope this helped you