Link category input field not showing parent category

I have a client using a category structure in which they have main categories with subcategories for each year respectively, ie.

Main category 1
2015
2016
2017
2018
Main category 2
2015
2016
2017
2018
Etc…

When using the input field in the category page (wp-admin/edit-tags.php?taxonomy=category) to sync categories with each other,
the list will render unusable when searching for category “2018” because I don’t know which one it is.