The lever arm is the distance from the attachment point (e.g. tree trunk) to the load application point (support & beam). The larger the lever arm, the greater the torque and thus the load on the fastener (here the connection tree bolt in the trunk). The pivot point of the tree bolts is approx. 4-8 cm inside the tree. A little experiment with the lever arm: Extend your arm sideways and your partner presses down with the same force, once at the elbow and once at the hand. When is the load on the shoulder greater?