Welcome to MusicBee and the forum millturn.
The first and most obvious path would be to make sure your classical music gets tagged with 'classical' as the genre, and then use that genre tag for further filtering and separating it from your non-classical music.
(Without going into too much details immediately, in case you would like to be more specific with genres and want to use genres such as 'Baroque', Romantic' etc. it would be better to use 'genre category' as the filter.)
You could use this kind of filtering, or you could create two different libraries for classical and non-classical.
For this, it would be best to have a separate root folder 'Classical' that you can scan and refer to.
Or, and this might sound a bit weird but I have been trying this out for a while now and I may stick to it:
Have two separate portable installations of MusicBee.
One for classical, one for non-classical.