public function build()
    {
        if (is_null($this->getParent())) {
            // Add a top menu page.
            add_menu_page(
                $this->getTitle(),
                $this->getMenu(),
                $this->getCapability(),
                $this->getSlug(),
                [$this, 'render'],
                $this->getIcon(),
                $this->getPosition()
            );
        } else {
            // Add a submenu page.
            add_submenu_page(
                $this->getParent(),
                $this->getTitle(),
                $this->getMenu(),
                $this->getCapability(),
                $this->getSlug(),
                [$this, 'render']
            );
        }
    }