Given a binary tree, find the level in the tree where the sum of all nodes on that level is the greatest.
1 Level 0 - Sum: 1
/ \
4 5 Level 1 - Sum: 9
/ \ / \
3 2 4 -1 Level 2 - Sum: 8
ccl -e "(ql:quickload :level-of-tree-max-sum/tests)" -e "(asdf:test-system :level-of-tree-max-sum)" -e "(quit)"