That is kind of a surprise
English is not my first language, so I might be imprecise. But, if you build the two trees as described in "The Task", they look like this:
T1: Mammal - Canine - Dog
T2: Mammal - Canine - Fox
To get from T1 to T2, you have to remove Dog and Wolf.
it doesn't benefit from extra confusion
Well, the tree structure was part of the class originally. I'll add that to the specification.
Update: I won't. It's not needed in the solution. You should use the documented API, i.e. Parent and get_leaves.