D8 override core class

Question

I am using SHS module. What I want to do is, override the SHS widget such that the I can alter the query used to fetch the data in the widget. Till now, I have overriden the route controller and have found that the underlying query is being generated from the loadTree() function of the core/modules/taxonomy/src/TermStorage.php file.

Now what basically I want is, to override this function, such that I may be able to alter the query to my requirement. Im not sure what is the correct way to do that in OOPS.

Please help.