insert() with typescript

[kandarp-codingscape]

Hello,
I'm new to Knex, and using typescript, and the following works:
knex.select().from<User>('tbl_user').first();
where Knex is able to map columns to the User interface.

I'm trying to do same with .insert() but a bunch of tries haven't worked out.
I've tried things like:

knex.insert(user).into<User>('tbl_user');
knex<User>('tbl_user').insert(user);

User has firstName and table has first_name. Searching other issues/docs and online. Can someone help/point me in the right direction?
Thanks!

Edit: I suppose this would've worked: https://knexjs.org/guide/#postprocessresponse but ended up using https://github.com/Kequc/knex-stringcase