custom-content-update.php

 public function include_files() {
      include_once('custom.html'); //path to your html file
  }
        
  public function add_custom_html() {
      global $post;
      $product_id = $post->ID; 
      $categories = get_the_terms( $product_id, 'product_cat' );

      if( empty ($categories)){
          return;
      }     
      
      foreach($categories as $cat){
          if( 'men' == $cat->slug ) {
          
             //include the html file here
              $this->include_files();
              
          }
      }
                
}