Merging 2 MLT files into a project

Newbie here. I have created two projects, therefore now have two MLT files. If I want to combine the two projects into one project, how best do I go about it.

I had opened the one MLT file. Then placed the cursor at the end of the clip in the timeline. Then opened the second MLT file, but it replaced the original project.

So what I want to know i show to merge two MLT files.

Many thanks!!!

File->Open MLT XML as Clip