How to add categori selection option in theme option?

I am trying to add a category option in my wordpress theme using option tree. I am using this code in theme-option.php

<?php

add_action( 'admin_init', 'custom_theme_options', 1 );

function custom_theme_options() {

    $categories = get_categories('hide_empty=0&orderby=name');
    $wp_cats = array();
    foreach ($categories as $category_list ) {
    $wp_cats[$category_list->cat_ID] = $category_list->cat_name;
    }

  $saved_settings = get_option( 'option_tree_settings', array() );

  $custom_settings = array(
    'sections'        => array(
      array(
        'id'          => 'general',
        'title'       => 'Home Page  Settings'
      )
    ),
    'settings'        => array(

      array(
        'id'          => 'Great-Product',
        'label'       => 'Great Product',
        'desc'        => 'select great Product category',
        'type'        => 'select',
        'section'     => 'general',

   'std' => 'Choose a category',
  'options' => $wp_cats
      )
    )
  );

  if ( $saved_settings !== $custom_settings ) {
    update_option( 'option_tree_settings', $custom_settings );
  }

}
 ?>

But it is not showing any category. Where is my fault? Please tell me.