fell

function fell()
  turtle.dig()
  turtle.forward()
  local height = 0
  while ( turtle.detectUp() ) do
    turtle.digUp()
    turtle.up()
    height = height + 1
  end

  for i = 1,height do
    turtle.dig()
    turtle.forward()
    turtle.turnLeft()
    for j = 1,4 do
      turtle.dig()
      turtle.forward()
      turtle.turnLeft()
      turtle.dig()
      turtle.forward()
    end
    turtle.turnRight()
    turtle.back()
    turtle.down()
  end
end

fell()