Family tree maker allows you to merge two trees and give a different name. For example, A wants to merge tree with B. A can merge and keep the name as AB1 or AB tree or AMB tree. If you want to sync your tree to ancestry, you will not be able to do this. I will explain this to you in detail why you cannot sync with the ID that you have from Ancestry. Ancestry.com is the website where you need to create your account and purchase their subscription.