Add sub menu in media tab in admin menu

functions.php

<?php

// check if function does not exists
if ( ! function_exists( 'rtmedia_add_admin_bar_media_sub_menu_for_upload' ) ) {
	function rtmedia_add_admin_bar_media_sub_menu_for_upload() {

		// Please change the page_slug if you want from here
		$page_slug = 'file-upload';

		// check if function does not exists and RTMEDIA_MEDIA_SLUG is alredy defined
		if ( function_exists( 'get_page_by_path' ) && defined( 'RTMEDIA_MEDIA_SLUG' ) ) {

			// get the page by slug
			$page_data = get_page_by_path( $page_slug );

			// check if the page exists.
			if ( is_object( $page_data ) ) {

				// check if the page id exists.
				if ( isset( $page_data->ID ) ) {
					global $wp_admin_bar;
					global $rtmedia;
					$page_id = $page_data->ID;
					$wp_admin_bar->add_menu( array(
						'parent' => 'my-account-' . RTMEDIA_MEDIA_SLUG,
						'id'     => 'my-account-media-' . $page_slug,
						'title'  => 'Upload',
						'href'   => get_permalink( $page_id ),
					) );
				}
			}
		}
	}
}
add_action( 'rtmedia_add_admin_bar_media_sub_menu', 'rtmedia_add_admin_bar_media_sub_menu_for_upload', 10 );

Please the above snippet in functions.php of child themes.