If you have a finished tree structure of pages (top page plus all its child pages) in a Dr.Explain project, and want to have a copy of it in another project, just open both projects and select the ROOT page in the TOC tree and select Edit > Copy.  Then go to the other project and position the cursor on the page that will be its parent page, and select Edit > Paste.

 

Not only does it copy the page and all its children, it also brings all the index entries from the original document to the new document.  Amount of re-work?  Virtually zero.