Here's how to make a copy of your tree:
1. Download/export a GEDCOM or FamilyScript copy of your tree. Lower left corner of window has a button for this function.
2. Back to home screen click on the [My Account] button (upper right)
3. Click on the [Create or import new family] button and upload the file you just downloaded.
4. Click on the [Rename] button as required to give it an appropriate name.
Now you can select this tree from the My Account screen and edit away.