Minecraft CC redwood/fir tree cutter. No fuel required.

-- Script created by Zehdari

-- Setting the height to 0
local height = 0

-- Creating the refuel function
local function refuel()
 if turtle.getFuelLevel() < 20 then
  for a = 1,16 do
   if turtle.getFuelLevel() < 20 then
    turtle.select(a)
    if turtle.refuel(a) then
     for q = 1, turtle.getItemCount(a) do
      if turtle.getFuelLevel() < 20 then
       turtle.refuel(a)
      end
     end
    end
   end
  end
  turtle.select(1)
 end
end

-- Saying that the script has started
print "Cutting..."

-- Creating the beginning cut function
local function cut()
 turtle.dig()
 refuel()
 turtle.forward()
 turtle.dig()
end

-- Creating the function to cut upwards, until reaching the top
local function detectup()
 while turtle.detectUp() do
  turtle.digUp()
  refuel()
  turtle.up()
  turtle.dig()
  height = height + 1
 end
end

-- Creating the function to turn once reached the top
local function turn()
 turtle.turnRight()
 turtle.dig()
 refuel()
 turtle.forward()
 turtle.turnLeft()
end

-- Creating the function to dig and go downwards
local function down()
 for i = 1,height do
  turtle.dig()
  turtle.digDown()
  refuel()
  turtle.down()
 end
end

-- Calling the functions
cut()
detectup()
turn()
down()
turtle.dig()

-- Info for the owner
print "Tree cut successfully."
print ("Fuel level is: "..turtle.getFuelLevel())