When Hallimasch or also called Common Honey Fungus, it is a mushroom that you can regard as an edible mushroom. But it is also a danger to trees.
Danger for trees
The common honey fungus grows mainly on wood. In the forest it can often be found on tree stumps. However, it can also spread to he althy trees. It probably has the nickname common because it settles unnoticed between the bark and trunk and spreads. When the fruiting bodies appear years later, it is already too late. Because then the honey fungus has already damaged the tree so much that it will not survive sooner or later.
Fighting Honey Fungus
The first thing you need to do against this fungus is to remove the fruiting bodies. The second - and you as a hobby gardener will certainly not like it, but which is essential - means clearing and destroying the tree including the root system. This is the only way to prevent it from spreading to other trees. If you do not remove the tree as described, then the fungus can spread further. As a result, more and more trees in your garden are affected by this fungus. Accordingly, they will all die off.