Here it is a year later, but I could use some clarification on this, myself. I am a paid Ancestry.com member accessing and building my tree on the website using a computer with a Windows Operating System. I too, have no file export option on the top right. Is there a difference between the website Ancestry.com and the Windows program, Ancestry Family Tree? Is that the "Family Tree Maker" software available from Ancestry.com?
My reason for splitting my tree off to a new tree is I had started building my wife's tree off of mine. While at my family grave site, we found one of my ancestors married to someone with a middle name matching my wife's maiden name. Sure enough, his middle name came from his mother's maiden name and since that name and spelling of it is fairly uncommon, we think my wife and I may not be the first "Storey/Huguley" marriage from both our family blood lines. Anyway, I'd have been better off building her's as a "new tree" as is the option from the ancestry web site.