Laravel 5.5 APK file uploading issue

In my project I am working with apk file to upload. In my controller I write

if ($request->hasFile('app_file')) {
        $apk_file = $request->app_file->store('app_file');
        $app->app_file = $apk_file;
    }

Upload works fine. But instead of .apk file it store as .zip. Till now I don't use any validation. Where is the actual issue? Thank you.

via Chebli Mohamed