Hide subdirectory from URL using .htaccess

I am working on a website project in which I want to hide the directory name. I have an HTML document in a subfolder like this. root/posts/hello.html

I want that when someone clicks on www.example.com/hello, then it actually shows www.example.com/posts/hello.html. But the browser must display www.example.com/hello in URL to the user. How can I achieve this?