So here are the results of adding over 127 children to one parent:
object_id | tree_sortkey
-----------+------------------------------------------------------------------
518 | 0000010000000000000000110000000001111100
519 | 0000010000000000000000110000000001111101
520 | 0000010000000000000000110000000001111110
521 | 0000010000000000000000110000000001111111
522 | 0000010000000000000000110000000010000000000000000000000010000000
523 | 0000010000000000000000110000000010000000000000000000000010000001
524 | 0000010000000000000000110000000010000000000000000000000010000010
525 | 0000010000000000000000110000000010000000000000000000000010000011
(134 rows)
So the pl code smoothly transitions to a larger key. Cool!