Futurology

They grow, build themselves out of carbon from the air. Live for a while (300 years for my local trees). Die, rot, release the carbon into the air; or they burn and release the carbon into the air

At best you replace forests we have destroyed and pull the same amount of CO2 out of the air as destroying those forests put in a hundred or more years ago. The main cause of carbon in the air is burning fossil fuels, so it won't help much.

If you're growing trees somewhere they could grow without special help (extra water, fertilizer) you're definitely growing trees humans removed in the past

You can do it by cutting down the forests you've grown, and regrow them over and over again and storing or processing the wood so it never rots