I always find it interesting to see how people deal with trees that are within their property.

Unusual growth at the base of a Rowan tree in Stoodley Glen, which has the appearance of a wasps’ nest. 
I wonder if over many years the tree has tried to form new shoots at the base as compensation for previous tree work and trunk removal.
The 2 stems and the high stem clearing of branches is evidence of this.

Nearby is this sycamore tree held captive by a shed. 

Rowan tree with basal bulge
Previous adventitious buds that were aborted and calloused by growth every year?