Stores the Tree
List < int > [ ] tr = new List < int > [ n + 1 ] ; for ( int i = 0 ; i < tr . Length ; i ++ ) tr [ i ] = new List < int > ( ) ; tr [ 0 ] . Add ( 3 ) ; tr [ 0 ] . Add ( 4 ) ; tr [ 4 ] . Add ( 6 ) ; tr [ 6 ] . Add ( 2 ) ; tr [ 2 ] . Add ( 1 ) ; tr [ 2 ] . Add ( 8 ) ; tr [ 8 ] . Add ( 5 ) ; tr [ 5 ] . Add ( 7 ) ;