Tree growth can give us information about climate, soil and other environmental factors that existed during the times of growth. Trees can certainly give insight into some of the conditions early humans must have experienced. Science has come a long way, and some of those tests can give us valuable information by studying tree rings, bark and fossils.
I don't know how much Trees can prove about early human life but we can rule out the biblical stories about the earth being only 3000 years old. There have been many trees found to be much older than that. If the entire earth really was under water for 40 days and 40 nights those trees would not be alive today. Trees cannot survive without sunlight while completely submerged far underwater.
When it really breaks down there is a bountiful amount of information to be found from these trees, I think the limit is finite, and can only really tell you about the outside factors and environmental changes of the world, but not necessarily what humanity as a whole was like.
While I'm sure the trees could reveal something about the atmosphere or pollen counts or some such thing about the world when civilization was evolving, what we don't know about the rise of the fertile crescent and Yangtze valley won't be filled in by felling ancient trees. And there are not trees alive that have been so since early human life, unless we are subscribing to strict Biblical timelines and disregarding all known science.