When a person shares with another, their feeling of self worth rises. It only takes one short climb to have a feeling of completion. Sharing with others is easier. It's much easier to share with others if you have a common ground to meet on. It's even more easy to share if the common ground is based on having fun together.
Comradeship replaces cliques.
This is achieved through sharing and common grounds. Competition is replaced with cooperation. Tree climbing is a sharing experience. It's not a competing experience. The fun is getting everyone up into the tree, not getting there first.