18 
 +---10 -L
 |    +--- 5 -L
 |         +--- 4 -L
 |         +--- 6 -R
 +---73 -R
      +---27 -L
      |    +---25 -L
      |    +---41 -R
      |         +---32 -L
      |         +---51 -R
      |              +---45 -L
      |              +---54 -R
      +---99 -R
