Mushrooms growing on trunk-base of JBP sapling

I just plucked them off 2-3 weeks ago (they were smaller then, about 1-2” in diameter). Saw there was a new, big one in the same exact spot this morning.

Should I be concerned?
Is it a fungal problem?
I always thought mushrooms on tree trunks were a bad sign of old/ancient trees dying or in decline or rotting (though this one is a young sapling).

How do I get rid of it for good?

Atm, I only have hydrogen-peroxide and horticultural/mineral-oil.
Will those work, or do I need something else like daconil, copper, etc.?

Mycorrhizae growing in the soil (from which mushrooms can blossom) can be beneficial to trees since they help the roots absorb nutrients. Don’t be so quick to eradicate them. Just make sure your soil has good drainage and don’t over water your trees.