Android Search Expandable ListView

I am building my first android app and I encountered a problem. In the app I have a search function that uses a ListView. Here users can search for a certain item and see if it exists. This works really well and I did it based on this tutorial: Android ListView with Search

All my items are found in a string array defined in array.xml. Now, every item can be part of one or more collections. Currently I show the collections it is included in next to the item's name, like this: "ITEM -> Collection(s)". This works but is not really an elegant option. What I would like to do is have the item's name as the ITEM in an expandable ListView and the collections it belongs to as a SUBITEM. I would therefore have 2 string arrays, one for the parent items, one for the children items.

All the examples I have found are populating the list "manually" and I can not figure out how to assign my ITEMS array to the GROUP and my COLLECTIONS array to the CHILDREN.

I don't know if I explained this clearly enough but in short, it would be like this:

ITEM_1 = 1st Group name
COLLECTIONS_1 = 1st Group's child

Example Image

Thank you!

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