+ /*
+ * For a btree shorter than the maximum height, the worst case is that
+ * every level gets split and a new level is added, then while inserting
+ * another entry to refill the AGFL, every level under the old root gets
+ * split again. This is:
+ *
+ * (full height split reservation) + (AGFL refill split height)
+ * = (current height + 1) + (current height - 1)
+ * = (new height) + (new height - 2)
+ * = 2 * new height - 2
+ *
+ * For a btree of maximum height, the worst case is that every level
+ * under the root gets split, then while inserting another entry to
+ * refill the AGFL, every level under the root gets split again. This is
+ * also:
+ *
+ * 2 * (current height - 1)
+ * = 2 * (new height - 1)
+ * = 2 * new height - 2
+ */
+