"...when confronted with several tree ring data sets, a "researcher" chose the set that reinforces the existence of global warming rather than average them all out or rejecting the extremes."

That seems to be true, but it is more complicated.

The assumption is that tree rings are wider in warmers years and narrower in colder ones.

Actually, the tree growth (as reflected by growth ring size), can change due to rainfall, nutrient availability, temperature, and probably CO₂ level plants take in as part of the cycle of photosynthesis.

Claiming that it is solely an indicator of global temperature is not science, it is politics.