pocketmine\block\Sapling::onUpdate PHP Method

    public function onUpdate($type)
    {
        if ($type === Level::BLOCK_UPDATE_NORMAL) {
            if ($this->getSide(0)->isTransparent() === true) {
                $this->getLevel()->useBreakOn($this);
                return Level::BLOCK_UPDATE_NORMAL;
            }
        } elseif ($type === Level::BLOCK_UPDATE_RANDOM) {
            //Growth
            if (mt_rand(1, 7) === 1) {
                if (($this->meta & 0x8) === 0x8) {
                    Tree::growTree($this->getLevel(), $this->x, $this->y, $this->z, new Random(mt_rand()), $this->meta & 0x7, false);
                } else {
                    $this->meta |= 0x8;
                    $this->getLevel()->setBlock($this, $this, true);
                    return Level::BLOCK_UPDATE_RANDOM;
                }
            } else {
                return Level::BLOCK_UPDATE_RANDOM;
            }
        }
        return false;
    }