Parameterized Tree Graph

;; add these features to your model

breed [terminal-nodes terminal-node]
breed [intermediate-nodes intermediate-node]
breed [centrums centrum]
turtles-own [level]

to setup
  __clear-all-and-reset-ticks
  if white-background? [ask patches [set pcolor white] ]
  create-random-tree population layers %-actors
  ask centrums [
    ifelse white-background?
      [ set color black ]
      [ set color white ]
  ]
end 

to go
  tick
end 

to create-random-tree [number-of-nodes levels %-terminals]
  set-default-shape turtles "circle"   
  create-centrums 1 [
    set color gray
    set level 1
  ]
  create-intermediate-nodes (number-of-nodes - (number-of-nodes * %-terminals) - 1) [  
    set color green
    set level 2 + random (levels - 2) 
  ]
  ask turtles with [breed != centrums] [
    ifelse any? turtles with [level = ([level] of myself - 1)]
      [ create-link-with one-of (turtles with [level = ([level] of myself - 1)]) ]
      [ create-link-with one-of centrums 
        set level 2 ]
  ]
  if count intermediate-nodes with [count link-neighbors = 1] > number-of-nodes * %-terminals [
    user-message (word "That's not enough terminal nodes for this graph.") 
    stop
  ]
  ask intermediate-nodes with [count link-neighbors = 1] [
    hatch-terminal-nodes 1 [  
      set color red
      create-link-with myself
      set level ([level] of myself + 1)
    ]
  ]
  let remaining-terminal-nodes number-of-nodes * %-terminals - count terminal-nodes
  repeat remaining-terminal-nodes [
    ask one-of turtles with [breed != terminal-nodes] [
      hatch-terminal-nodes 1 [  
        set color red
        create-link-with myself
      set level ([level] of myself + 1)
      ]
    ]
  ] 
  layout-radial turtles links one-of turtles with [breed = centrums]
end