I don't know if you are still looking for an answer, but it is possibly to create multiple trees on one account.
After logging in you should be able to see all your trees. There is a button at the bottom saying "Create or import new family" clicking on that wil bring you to a clean tree, where you can make the other family tree.
To switch between them click on the "account" button at the top right while working on your tree. You'll get to your list of trees, you can also rename them to make it easier to remember which is which.
I hope this helped. If you need more help, let me know.
