Custom customer multiselect attribute with options in database

I need to create an extension that will store options of multiselect customer attribute in the database. There are many answers of how to create multiselect customer attribute, and all of them show how to store options in the file, but none how to store in the database. I tried to find similar functionality in magento2, but customer doesn’t have multiselect attribute.

InstallData.php:

namespace VendorExtensionSetup;

use MagentoEavModelConfig;
use MagentoEavSetupEavSetup;
use MagentoEavSetupEavSetupFactory;
use MagentoFrameworkSetupInstallDataInterface;
use MagentoFrameworkSetupModuleContextInterface;
use MagentoFrameworkSetupModuleDataSetupInterface;

class InstallData implements InstallDataInterface
{
    private $eavSetupFactory;

    public function __construct(
        EavSetupFactory $eavSetupFactory,
        Config $eavConfig
    ) {
        $this->eavSetupFactory = $eavSetupFactory;
        $this->eavConfig = $eavConfig;
    }

    public function install(
        ModuleDataSetupInterface $setup,
        ModuleContextInterface $context
    ) {
        $eavSetup = $this->eavSetupFactory->create(["setup" => $setup]);

        //magento 2 create customer dropdown attribute programmatically

        $eavSetup->addAttribute(
            MagentoCustomerModelCustomer::ENTITY,
            "custom_multiselect",
            [
                "label" => "Customer multiselect segment",
                "system" => 0,
                "position" => 800,
                "sort_order" => 800,
                "visible" => true,
                "note" => "",
                "type" => "text",
                "input" => "multiselect",
                "source" => "VendorExtensionModelSourceCustommultiselect",
            ]
        );

        $this->getEavConfig()
            ->getAttribute("customer", "custom_multiselect")
            ->setData("is_user_defined", 1)
            ->setData("is_required", 0)
            ->setData("default_value", 22)
            ->setData("used_in_forms", [
                "adminhtml_customer",
                "checkout_register",
                "customer_account_create",
                "customer_account_edit",
                "adminhtml_checkout",
            ])
            ->save();
    }

    public function getEavConfig()
    {
        return $this->eavConfig;
    }
}

Custommultiselect.php

namespace VendorExtensionModelSource;

class Custommultiselect extends
    MagentoEavModelEntityAttributeSourceAbstractSource
{
    public function getAllOptions()
    {
        if ($this->_options === null) {
            $this->_options = [
                ["value" => "1", "label" => __("default")],

                ["value" => "2", "label" => __("Test")],

                ["value" => "3", "label" => __("Test2")]
            ];
        }

        return $this->_options;
    }

    public function getOptionText($value)
    {
        foreach ($this->getAllOptions() as $option) {
            if ($option["value"] == $value) {
                return $option["label"];
            }
        }
        return false;
    }
}

So basically I need to store: default, Test, Test2 in the database, for example here eav_attribute_option

Any help would be appreciated.