Filtering second level index words in HTML5 output?

[StudioSm]

I am running FrameMaker 2017.

I have a book with an index. The index contains index words in two levels, like:

Monkey

     Gibbon

     Chimpanze

     Gorilla

When i convert the book to HTML5 using FrameMakers publish feature, I get a nice html5 file.

The html5 version of the index I am able to filter the words (keywords) in the index. But only first level keywords - like "Monkey" in my example. The keywords like "Gibbon", "Chimpanze" are not filtered.

My questions are: Why are these second level keywords not filtered and - is there a way to include them in the filtering besides making them firstleve keywords?

[Jeff_Coatsworth]

First I would test using another layout to see if the search will find your sub-terms. If that gives the same result, I suspect your only solution is to do extra entries like "Gorilla - see Monkey"