Alexa code needed for separate sub directories?

Alexa code needed for separate sub directories?

I have a PHP website, the home page is totally separate thing from the sub
directories, i.e site.com
and sub dir are
site.com/class1
site.com/class2
site.com/class4
Now, I want to put in alexa into my website, I uploaded the alexa
verification file into my root folder. So, do I have to provide alexa code
for each sub directory or the alexa file in root directory can do the
magic?
Logically, I must provide code for all directories but I am still curious
to know.