Hi,
thanks for your question, and sorry for the trouble.
Unfortunately, as the layout of the Advanced Editor is coming directly from WordPress, I can not add extra buttons to it.
You can however easily create lists by using HTML directly, e.g.
<ul><li>item 1</li><li>item 2</li></ul>
for an unordered list, or
<ol><li>item 1</li><li>item 2</li></ol>
for an ordered list.
(Just be careful and don’t put line breaks between the HTML tags.)
Regards,
Tobias