In their natural form, you are correct. But if you cut down those trees and put them in Wood Vaults, specially engineered enclosures to ensure anaerobic environments, thus preventing wood decay -- then you would properly sequester the carbon. That is literally what happened in the carboniferous period that caused all the trees to turn into coal.

There is recent research on this that indicates we could achieve a 10 gigaton annual sequestration rate with only a 5% impact on the total terrestrial tree production and at a cost of $30/ton.[1]

"The quantity of this wood utilization can be controlled carefully to maintain a desired amount of CO2 in the atmosphere to keep the Earth’s climate from diving into the next ice age, acting as a climate thermostat."

[1] https://cbmjournal.biomedcentral.com/articles/10.1186/s13021...