IIUC the markdown spec followed in CommonMark.jl is more robust and may potentially replace Markdown.jl as the default in the stdlib one day. So I would probably just use that instead:
julia> using CommonMark
julia> cm"""
- a
- aa
- aaa
- aab
- aac
"""
● a
○ aa
▶ aaa
▶ aab
▶ aac