Currently (Dec 2019), Webflow does not support embedding Collection Lists within other Collection Lists. However with a bit of design planning, you can create this effect functionally in your finished website with a bit of HTML tagging, and a small piece of Javascript.
IMPORTANT, this will only work if your two collections are connected with a Reference field, in which the child node identifies its parent node. A good example of this is venues & events - each event must be in one and only one venue.
Here’s the original post, which contains a writeup of my solution;
And here’s a blog article I’ve finally gotten around to writing, which contains;
- A video walkthrough of the solution and how to implement yours
- A demo Webflow project so you can see the solution in action