How to put a site in a site?

Question

Apache HTTP Server

Hello. In general, perhaps a stupid question, but I didn’t google the norms of information and I want to ask how other people do it.
In general, the situation is this, given:
1 server, let's say 10.10.10.10
On the server, there is a linux with Apaches. At this address, we get access to the www/html folder.
This is where the question begins. Let's say I want to put a site in a site. My base is in the html folder, but the second site is in html/site2
Every time you have to take a steam bath with include and required. The more pages, the more difficult and after a couple of hours the devil will break his leg with these ../../../include and so on) In general, how do you manage the base directory of the site itself. Or there are no universal ways, they say to prescribe for one site to take all include from a given directory, and for another site another directory. Terribly poorly written question, but I hope you understand my nonsense)