Here's the feature:
The user is a construction sub-contractor. Each user specializes in something like welding or plumbing or windows, etc... Now, these things they specialize in are formally defined in an industry standard hierarchical structure. The hierarchy has 5 levels and contains thousands of entries.
I want the user to be able to specify their specialties from this structure, but I think a tree-view with checkboxes and thousands of items will be horrible from a UX perspective, especially on mobile devices. What I am thinking is more along the lines of a textbox with "auto complete" so that when they start typing: "weld.." a dropdown appears with all of the specialties beginning with "weld". If they select a higher level specialty then all contained sub specialties are selected too.
Please advise on your suggestions for the best user experience here and keep in mind a mobile-first / responsive design.