--- |
  0
--- |+
  1
--- |-
  2
--- |
  3

--- |+
  4

--- |-
  5

--- |
  6


--- |+
  7


--- |-
  8


--- |
  9
    
--- |+
  a
    
--- |-
  b
    
--- |
  c
    
    
--- |+
  d
    
    
--- |-
  e
    
    
--- |
  f

  f
--- |+
  g
    
  g 
--- |-
  h

  h
--- |
  i
    
  i
--- |+
  j
    
  j 
--- |-
  k
    
  k
--- |
  l

   
     
   

--- |+
  m

   
     
   

--- |-
  n