Cart.php
public function add(CartItemInterface $element, $save = true): self
    {
        $this->addItem($element);
        $save && $this->storage->save($this);

        return $this;
    }
public function add(CartItemInterface $element, $save = true): self
    {
        $this->addItem($element);
        $save && $this->storage->save($this);

        return $this;
    }
Add an item to the cart

@param models\CartItemInterface $element
@param bool $save

@return $this