LumberJack

function chopStraightUp()
    --Get itselft beneath target trunk
    turtle.dig()
    turtle.forward()

    --Chop until tree top
    while turtle.detectUp() do
        turtle.digUp()
        turtle.up()
        while turtle.getFuelLevel() < 1 do
            turtle.refuel(1)
        end
    end

    --Move Down to ground level
    while not turtle.detectDown() do
        turtle.down()
        while turtle.getFuelLevel() < 1 do
            turtle.refuel(1)
        end
    end
end

local treeNumber

print("How many trees?\n")
treeNumber = tonumber(read())

while turtle.getFuelLevel() < 1 do
    turtle.refuel(1)
end

local i
local j
for i = 0, treeNumber-1 do
    --Find tree
    while not turtle.detect() do
        turtle.forward()
    end

    --Chop two trunks down
    for j = 0, 1 do
        chopStraightUp()
    end

    --Make 180 turn
    for j = 0, 1 do
        turtle.forward()
        turtle.turnRight()
    end

    --Chop other two trunks down
    for j = 0, 1 do
        chopStraightUp()
    end

    --Make 180 turn
    for j = 0, 1 do
        turtle.forward()
        turtle.turnRight()
    end
end