Adding a custom cart negative fee tax issue in woocommerce

I have a shipping discount in my woocommerce site, I would like to show it on cart page and checkout page, for that I used add_fee() method.

WC()->cart->add_fee( 'Shipping Discount', -20, false );

It subtract 20 from total amount, but when I go to check order in orders inside admin it gives discount on tax too according to tax rate I configured. Is there any alternative to add discount

How can I do this in woocommerce?