>any ideas

because tree is so old and has so many cognates in other languages, it may be hard to say much more than "tree is a very old word (ca. 825CE) which has many cognates in other languages."

O.E. treo, treow "tree" (also "wood"), from P.Gmc. *trewan (cf. O.Fris. tre, O.S. trio, O.N. tre, Goth. triu), from PIE *deru- "oak" (cf. Skt. dru "tree, wood," daru "wood, log;" Gk. drys "oak," doru "spear;" O.C.S. drievo "tree, wood;" Serb. drvo "tree," drva "wood;" Rus. drevo "tree, wood;" Czech drva; Pol. drwa "wood;" Lith. derva "pine wood;" O.Ir. daur, Welsh derwen "oak," Albanian drusk "oak"). [online etymology dictionary]