Each topic line can begin with one or more '-'s. The more '-'s, the lower it will be in the hierarchical structure.
Example:
* Title of Slide 1
- 1. the first topic inside Slide 1
-- 1.1. the sub-topic of 1
--- 1.1.1 the first sub-sub-topic of 1
--- 1.1.2 the second sub-sub-topic of 1.
* The second slide
- some topics inside