peak; mountaintop (almost always in a figurative sense)
When my father was young, a government job represented the pinnacle of success for a man of his background.
pinnaculum (peak, pinnacle, gable) (Latin)
epitome, pinnacle, zenith
pin (PINE TREE)+NACLE. SOUNDS LIKE UNCLE. so your uncle wants to CLIMB the PEAK OR HIGHEST POINT OF PINE TREE.