Admin Interface: Business Classification

I'm working on an admin interface for managing hierarchical data (drill down).

Now you have to link "item a" to multiple business classifications, there are around 1400 according to the Dutch Chamber of Commerce.

Let's say "item a" has to be linked to half of the Business Classifications, that would be 700 checkboxes. A lot of clicking and a loss of overview is imminent if we would proceed with checkboxes. To be honest I don't consider this a valid option.

A Business Classification has a unique number A Business Classification has a subsector A subsector has a sector

The list Business Classifications (https://www.kvk.nl/download/SBI_code_%20ENG_2018_dec2017_tcm109-451911.pdf)

Other options: - dual list box (https://www.virtuosoft.eu/code/bootstrap-duallistbox/) - filling in ranges like print dialog (1-100, 110, 115, 200-900) - drill down on sector and subsector

My question is, are there other solutions / examples? How can I solve this with maintaining overview.