k = 1  ->  2
k = 2  ->  3
k = 3  ->  4
k = 4  ->  6
k = 5  ->  7
k = 6  ->  9
k = 7  ->  13
k = 8  ->  15
k = 9  ->  17
k = 10  ->  18
k = 11  ->  20
k = 12 ->  the tree has fewer than k keys
