Align two columns in one page and each topic title on the top of the page

Hello all.

I created a book map with two chapters whick contain 4 or more topics in each and it is going to be published in PDF format.
Then, to save the number of page, I am trying to show two columns in one page and each topic should start from the top of the page.

However, Arbortext Styler does not have such function in its UI.

I am wondering if this can be achieved with some souce editting.

Do you know any source edit that works for this problem?

Thank you for your time.

Best wishes,

Tomomi