By the time we research some Level 2 and 3 infrastructure within an infrastructure family, we may not have built the Level 1 version of infrastructure yet, and it's not immediately obvious that we're missing out on building higher level ones when we glance at a city's construction list.  For example, I may have a city with a ton of naval trade routes leading to it, but just one harbour.  With only one harbour, it's not worthwhile for me to build the Fishmonger infrastructure (it's only +3 Money), but once I research Seafaring Mastery, I'm really going to want to build that Great Fishmarket, which could be worth 10s or even 100s of money, but it's easy to miss that I'm missing the prerequisite.

There are two ways to make it easier to spot these incomplete family trees, and either one of them would be very helpful to add to Humankind:

1. Show all the infrastructures that I have researched in the construction list, but show them as unbuildable until the prerequisite is built.  For example, once I researched "Seafaring Mastery", the Great Fishmarket would appear immediately after the Fishmonger, but it would be unbuildable until I build the Fishmonger.  The help text would say something like "You cannot build this infrastructure until you complete the previous infrastructure within this family." (These unbuildable infrastructures could also appear/disappear when we toggle the "Only Buildable" switch)
2. Mark the infrastructure in the construction list with an icon when later infrastructure in the same family is available.  In this example, only the Fishmonger would appear in the construction list, but it would gain an icon as soon as I research the Great Fishmarket, and now the unbuilt Fishmonger is a prerequisite for another unseen infrastructure.   Maybe the icon would be a blue, green, or yellow "up arrow" similar to units that have an upgrade available to them, because this is a similar idea.

Humble bump for what I think is still a useful UI improvement.

Realy cool idea. In addition i can suggest to add filters in this list. for example, show only infrastracture that give production, because this is first thing you want to build, because it make building other infrastructure faster