Add sub menu in media tab of admin menu

functions.php

<?php

// check if function does not exist
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 RTMEDIA_MEDIA_SLUG is already defined
		if ( defined( 'RTMEDIA_MEDIA_SLUG' ) ) {

			global $wp_admin_bar;
			$wp_admin_bar->add_menu( array(
				'parent' => 'my-account-' . RTMEDIA_MEDIA_SLUG,
				'id'     => 'my-account-media-' . $page_slug,
				'title'  => 'Upload',
				'href'   => trailingslashit( get_rtmedia_user_link( get_current_user_id() ) ) . RTMEDIA_MEDIA_SLUG . '?' . $page_slug . '=1',
			) );
		}
	}
}
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.