How to insert indent in markdown

Question

I want to make the format of my text just as below by using markdown:

how could i write the markdown file?

Answer 1

 1. 1
 1. 2
   1. 1
   1. 2
 1. 3

outputs

1. 1
2. 2
   1. 1
   2. 2
3. 3

the sub-numbers 2.1. is not super easy to achieve in HTML, that's the limitation here.