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.
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 your new tree.