将主域重定向到3级子文件夹而不更改URL

Let's say my domain is mydomain.com My structure is root>subfolder1>subfolder2>subfolder3>index.php How can I redirect domain so that mydomain.com points to subfolder1>subfolder2>subfolder3>index.php without changing url? I have a htaccess in subfolder3 which takes care of parsing url so it has to be unchanged.Let's say my domain is mydomain.com My structur