Kara walks around the trees in an endless loop. In each step, he considers the sensors "tree front?" and "tree right?" to determine the appropriate action.

while true
  if kara.treeFront and kara.treeRight
    kara.turnLeft
  else
    if not kara.treeFront
      if kara.treeRight
        kara.move
      else
        kara.turnRight
        kara.move
      end
    end
  end
end