Unable to get parent id in sub category seeding in Laravel

I need to create seeds in Laravel. i have two tables as setting_categories and settings. Table schema as below.

I have added seeds in setting_categories successfully.

I am trying to seed for settings table as below

<?php

use Illuminate\Database\Seeder;

class Settings_v_1_0_Seeder extends Seeder
{
    /**
     * Run the database seeds.
     *
     * @return void
     */
    public function run()
    {
        DB::statement("TRUNCATE TABLE settings");

        //$site_setting_id = SettingCategory::select("id")->whereSlug("site_settings")->firstOrFail();
        $site_setting_id = App\SettingCategory::where('id', 1)->get()->first();

        $settings = array(['created_at' => date("Y-m-d H:i:s"), 'updated_at' => date("Y-m-d H:i:s"), 'setting_category_id' => $site_setting_id, 'code' => 'site_name', 'value' => 'test', ' sort_order' => 1],
                            ['created_at' => date("Y-m-d H:i:s"), 'updated_at' => date("Y-m-d H:i:s"), 'setting_category_id' => $site_setting_id, 'code' => 'header_caption', 'value' => 'test', ' sort_order' => 2],
                            ['created_at' => date("Y-m-d H:i:s"), 'updated_at' => date("Y-m-d H:i:s"), 'setting_category_id' => $site_setting_id, 'code' => 'site_msg', 'value' => 'test. Copyright 2018 - 2018  &copy;', ' sort_order' => 3]
                        );

        DB::table('settings')->insert($settings);
    }
}

But it is throwing error as

Symfony\Component\Debug\Exception\FatalThrowableError : Class 'App\SettingCategory' not found

In the commented line I used $site_setting_id = SettingCategory::select("id")->whereSlug("site_settings")->firstOrFail(); as well. But no luck.

Could someone please suggest.

via Chebli Mohamed