Unity Container with Composition Root

I am new to DI and unity container. I am trying to use Unity with Composition Root. I have all my unity mappings/registrations in app.config file and just want to centralise all the resolve calls for my application.

The Application has many classes and very nested object graph created using constructor injection. So in a centralise location I want to create this object graph and then start make the call to do the actual work.

Please suggest a good way to implement composition root with unity.

Thanks!