ya light. as with many cactus, especially the vine species of cactus they will etiolate up and up with super thin stems and many aerial roots clinging to what they can until they hit real sun, then they umbrella and fill out and can start thinking about flowering. trees make good poles, but not trees with real canopies. telephone poles and betel nut trees are prime examples of what light is needed, but hack them down to harvest height as mentioned is needed.
avacado is way too much shade as a free standing tree. against a wall and pruned not sure, but the cactus needs good strong light.