to setup
  ca
  crt 1
end

to go
  ask turtles [pd back 5 set color blue tree 5 30]
end

to tree [len angle]
  if (len > 0.1)
    [fd len
     lt angle
     tree len * 0.6 angle
     rt angle * 2
     tree len * 0.6 angle
     lt angle
     back len
     ]
end