If there are things that look like black bootlaces by them, it could be honey fungus, which is bad news.

Fungus on trees is usually not good. You could post a photo for us to see. Or ask a good tree surgeon to take a look at it. You may need to remove the tree if it proves to be dangerous.

Are the fruiting bodies (Mushrooms/Toadstools) coming from the roots or the main stem?

If from the roots, as Doctorbob1 says, it may be Honey Fungus which wouldn't be the best case scenario. There are of course species that are symbiotic with the tree and periodically produce fruiting bodies too. These of course being symbiant, they are good for the tree and indeed help it obtain nutrients from the soil. You really need a positive id though as there are many, many species of fungi that could potentially fit the bill.