How to include ExpandableListView in ExpandableListView

Ex ExpandableListView (id:test1)
②ExpandableListView (id:test2)

が is not displayed.
①If you put を and 記載 in the same xml file, it will be displayed without any problems.

If you put を in の,

valtest1=requireView().findViewById(R.id.test1)

→Get it without any problems

valtest2=requireView().findViewById(R.id.test2)

→ View is null when viewed in debug mode and cannot be retrieved