I have a large established tree in my garden which I think is a bottlebrush of some kind (perhaps you can tell me what it is). Some of the upper branches are covered with a black, charcoal-like substance. Within the charcoal are shiny red bumps that look like sap. Is this a plant disease of some kind? See photo. As far as I know, the tree has not been set on fire or anything. Most of the other branches are fine and the tree seems otherwise healthy. It is currently flowering with fuzzy purple flowers.