This would be an actual (intelligently designed) code in the same sense as computer code or the Genetic code.
Of course the tree’s rings all by themselves tell us of it’s climactic history. The rings thickness are therefore essentially messages about the conditions that affect the growth rate in past seasons. You could consider them “codons” for growth seasons.
Absurd.
Codons are instructions that the translation process uses to produce a protein. They are functional sequences.
Nothing uses tree rings to do anything. We can only infer knowledge of the tree’s history through study.