They really look like old men that have lived through a lot.
The last looks like a very old wizard, the long-grey-or-white-hair-and-beard type. I might call him Merlin. He’s probably their leader, that is, if trees have leaders at all.
An old wizard brings to mind Gandalf from Lord of the Rings and that series, of course, has tree-like beings, ents. Maybe that’s what they really are?
Pictures are from Heaton Park.