Trees are wonderful for a number of reasons, and the need for them for local climate, which includes shading and their contribution to local humidity, is important as well.

They are not, though, a significant sequestration for CO₂.

A helpful way to think about this is to consider coal. To produce coal the energy input comes from time, pressure, etc over tens to thousands of millions of years.

The significance of trees is for the local climate, or global if you are considering one of handful of rainforests.