I am debugging my solution against already accepted solutions for this problem, by creating large test cases. I have found something weird. Some solutions are considering even the trees which are either (< l) or (> r). I have one testcase which proves this.

testcase link : https://drive.google.com/file/d/0B088hEdwtfVCSG5KNTl1M3REdUk/view?usp=sharing -> Query is (35916, 35926). you can check from the relation ship edges (by running a loop on them) that there are only three relationship edges which are useful for this query which are [(35922, 35924), (35923, 35925), (35925, 35926)]. using this answer will be 8, but answer from accepted solutions is 9. Even manually answer is 8. Can someone please explain the problem here ?

here is link to my solution : http://mirror.codeforces.com/contest/763/submission/27576175