Manually Add Drop Down in Navigation Bar

I can easily create pages/sub-pages and have the drop-downs appear in the navigation bar.

I want to make my navigation bar show only posts, and manually enter “sub-posts” that show as dropdowns. I know how to add links to the navigation bar, but how do I manually create a drop down that is attached to that particular post title?

For example, I want to have a post titled “Baseball” which shows in the navigation bar, and when the mouse hovers over it, a drop down would appear that says “Spring”, “Fall”, etc.

Note: I know using the Page/Sub-Page option is the quickest/easiest, but due to a few issues with galleries, etc that only function with posts, I want to make my navigation bar shows posts and “sub-posts” in a drop down fashion.