doc/images/tree.txt

   1        *
   2        |
   3        |0
   4        |
   5        V
   6        i
   7        |
   8  +-----+-----+
   9  |     |     |
  10  |0    |1    |2
  11  |     |     |
  12  V     V     V
  13  j     S2    j
  14  |           |
  15  |0       +--+--+
  16  |        |     |
  17  V        |0    |1
  18  S1       |     |
  19           V     V
  20           k     S4
  21           |
  22           |0
  23           |
  24           V
  25           S3