add_google_analytics_to_wordpress.php

<?php
add_action( 'wp_head', 'musilda_ga_code' );
function musilda_ga_code(){
  ?>
  <!-- Global site tag (gtag.js) - Google Analytics -->
  <script async src="https://www.googletagmanager.com/gtag/js?id=UA-169040585-1"></script>
  <script>
     window.dataLayer = window.dataLayer || [];
     function gtag(){dataLayer.push(arguments);}
     gtag('js', new Date());
     gtag('config', 'UA-169040585-1');
  </script>
<?php
}