Yes, you can, though this will need a few steps. First, you'll need to open the family tree you want to copy, and then click on the "Save" button on the bottom side of your screen. You'll have the option to download the family tree in different file formats, and should probably choose GEDCOM (however, to protect privacy, this format won't allow you to save/copy personal information such as phone numbers or E-Mail addresses if you use them).
Now, you'll want to go to your account page. You get there by clicking on the "My Account" button on the upper right side of your screen (close by "Save" and "Logout"). Now you'll see your username. E-Mail address etc., as well as an overview of all the families you've created. Below them, you can click on "Create/import new family".
This will create a new family tree. Instead of building a new family, there is a button on the left side (in the grey sidebar where you usually enter a person's personal info) that allows you to import a family tree instead of creating one from scratch. If you click on this button, you'll be able to select the GEDCOM file you downloaded earlier and upload it, effectively creating a clone of your original family tree.
Hope this helps!
