How to correctly set the default directory for multisite?

Question

1C-Bitrix

Multilingual project, where two languages ​​are used, based on multisite on one domain. Bitrix edition Business

At the root of the site are the folders ru and en
ru - Russian-language site
en - English-language site

Tell me how to correctly specify the path to the site folder so that when accessing the browser line http://my_site/ by default, the project from the ru folder is displayed?

Now sections of the Russian-language site are displayed at http://my_site/ru/contacts/ - contacts
http://my_site/ru/ - main page

How to make it so that files and folders from the directory are displayed when accessing http://my_site/ ru?