Sometimes some roadmap items are dependent on other ones and this needs to be shown with a clear visual indication.  There is an easy visual way to show these.

Dependency Milestones

Make a milestone type that will be used specifically for dependencies

In the timeline, make a new milestone to indicate the target or recipient of the dependency and then put that dependency milestone so that it sites on the front or back of the relevant item.

It will look something like this:

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