Show Titles in Sidebar

http://codex.wordpress.org/Template_Tags/wp_get_archives

See the info on ‘postbypost’ for the ‘type’ parameter.

Hi, my site is like a book with the CATEGORIES as CHAPTER TITLES. But I want to show the titles of the sections (posts) of each chapter (categories) to appear in the sidebar in consecutive manner with the first chapter at the top of the list, LIKE THIS:

CHAPTER 1
SECTION 1
SECTION 2
SECTION 3
CHAPTER 2
SECTION 1
SECTION 2
SECTION 3

Please help! Thanks.