For the example you’re using (ie www.mysite.com/pagebase/page1) you can:
- create a page called pagebase
- create a page called page1 and make pagebase the parent page – the url for this page will be www.mysite.com/pagepage/page1
This does mean that www.mysite.com/pagebase also exists as a browsable page, but I generally use that as a section description and section index page.