[Tree][NFC] Add some comments in GetLeafImpl
[Tree][NFC] Add some comments in GetLeafImpl

root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root