Is there a way to keep a custom menu expanded when editing a custom post type?

I am building a plugin that has a custom menu with pages under that menu. A few of those pages are custom post types. I would like to have the main menu stay open when I am on one of those custom post types. Is that possible?

Here is what the menu looks like when I’m on a non-custom post type page:

But when I click on Makes, Models or Types, the “Squirrels” menu closes because those are managed by the custom post type system.

Sorry if this is a duplicate. I looked through some similar questions but didn’t see one that had exactly this same issue.

Thanks!

I figured this out by putting the main menu slug into the show_in_menu key of the custom post type array like so:

$args = array (
        'labels' => $labels,
        'hierarchical' => FALSE,
        'description' => $title . 's',
        'supports' => array( 'title' ),
        'show_ui' => TRUE,
        'show_in_menu' => 'squirrels_inventory',
        'show_in_nav_menus' => TRUE,
        'publicly_queryable' => TRUE,
        'exclude_from_search' => FALSE,
        'has_archive' => TRUE
    );