When I see signs of evidense of tree worship in any religion, particularly the oldest known, I tend to think that these beliefs probably preceded that particular religion and that these beliefs are perhaps even older than sun worship beliefs.
This is going to sound silly, but bare with me. If a squirrel suddenly started worshipping something and adopted a religion, would he not be worshipping a tree? The tree is his home, his source of food, his shelter from those who prey on him. If one day he stopped taking his world for granted, he would say something like "I better show this tree I am grateful."
Ok that was a pretty big leap, but I hope my idea came across.