F.E. Doesn't have a "Save as..." function. You can make a duplucate tree manually as follows:
Download a GEDCOM or FamilyScript backup file (button at lower left)
Click on the [My Account] button (upper right). Then click on the [Create or import new family] button. Then click on the [import GEDCOM or FamilyScript...] button and load the file you created. Select a "Me" person then rename the tree as desired on the My Account page.
Also note that picture data is not included in these backups. If you don't have your own backups for the pictures, you can download the HTML file that will contain the picture data. You can extract the picture data manually when you view the HTML file in your browser into separate files that can be added to a new tree.
