Two private trees-can't work between them?

Hi--Posted this to the Ancestry tree message board but no one seemed to be able to figure this out, so hope this will make sense to someone here who can help me:
I don't know if this is the right board to post this query, but here goes---I purchased the FTM12 almost a year ago for the synch function. Unfortunately I quickly found that my home tree could not be linked to my existing tree on Ancestry.com so uploaded a new tree. Since I did not keep my home tree & Ancestry trees always completely up to date with each other, there was lots of info in one and not the other so at first all was going along fine and I was able to use my old tree to add any missing info to my new tree, but since Ancestry.com removed that function on private trees I am no longer able to "add this person to another tree". I thought that I would try making my "old" tree briefly public in order to take media items and persons from it and add to the new tree, but that did not seem to fix the problem either unless there is some kind of delay in doing this. Does anyone have any answers or suggestions on what to do? By the way, the trees have approximately 20,000 persons or more. Thanks, Cindy