What you can do, is this wiki code:
* Bullet Point Level 1, first line
* Bullet Point Level 1, first line \\ Bullet Point Level 1, second line
* Bullet Point Level 2
* Bullet Point Level 2
* Bullet Point Level 1, first line
Result see below.
But as far as I know, for your "Bullet Point Level 1, third line" there is no HTML equivalent. Therefore, you can not implement this in DokuWiki. (With a certain effort and tricky CSS maybe a simulation of it.)
Edit: @pop presents such a simulation - see below.
HTH - Michael Sy.