Please help identify tree disease
we have had a beautiful lilac tree for over 25 years, this year it blossomed as usual but we noticed the leaves were turning brown from the tips early. In the last 2 weeks a fungus has appeared on the trunk and some branches which looks like expanding foam in texture shape and colour (pale yellow) and now it's turning beige. We've been told it may be honey fungus, but can't find a picture on the internet of honey fungus that looks anything like this, can anyone help confirm? Or offer a second opinion as I know if it is indeed honey fungus i need to fell and burn the tree - but it's such a beautiful thing I don't want to base it's fate on a single opinion - I have attached pictures, thank you in advance.
P.S - I am a novice gardener so any advice in idiot format is greatly appreciated ????