Currently, there is not copy-paste or a specific task hierarchy import feature. There is a way to do something similar. It uses the Tools | Projects menu item. This was built to allow importing a project from another source - most commonly Microsoft Project. However, once the project plan is imported, the project link can be deleted, leaving only the task hierarchy.
MS Project is the easiest way to do this. But if you do not have MS Project, registered users can use the "Generic Project Management Interface" downloadable from our website here -
http://www.magsoftwrx.com/downloads.htm. It allows you to define a project as a Comma Separated Values (CSV) file. The file can be created manually, or using TT&E through a creative use of a Summary report Export. You can find details in the help file installed with the interface.