Then, aged 35, sitting under a tree at the place now known as Bodh Gaya (south of Patna), he vowed to stay there until his goal was achieved.
He never sat under any tree during his lifetime. 
mnli hypothesis: He never sat under any tree during his lifetime.  premise: Then, aged 35, sitting under a tree at the place now known as Bodh Gaya (south of Patna), he vowed to stay there until his goal was achieved.