Insertion: rotations needed to add one key to a Fibonacci tree
  height   nodes   rebalance events   single rotations
       4      12                  1                  1
       7      54                  1                  1
      10     232                  1                  1
      13     986                  1                  1
      16    4180                  1                  1

Deletion: rotations needed to remove the largest key of a Fibonacci tree
  height   nodes   rebalance events   single rotations   lg(n)
       4      12                  2                  2      3.6
       7      54                  3                  3      5.8
      10     232                  5                  5      7.9
      13     986                  6                  6      9.9
      16    4180                  8                  8     12.0
