itemize

[monty]

I want to get this with the itemize:

1. Item 
        1.1 Sub-item
        1.2 Sub-item
2. Other item
        2.1 etc.
        2.2 etc.

But when i increment the depth of the paragraph i get:
1. Item
        (a) sub-item
        (b) sub-item

¿any idea?