@rshaghoulian..clear solution and easy to understand... I have a doubt that there is no need to remove the reverse edges if we skipped adding them...

(i.e) if we skip this segment

        /* Edges are undirected: Add 2nd direction */
        HashSet<Integer> vNeighbors = map.get(v);
        if (vNeighbors == null) {
            vNeighbors = new HashSet<>();
            map.put(v, vNeighbors);
        }
        vNeighbors.add(u);

we need not do this..

        map.get(treeNum).remove(parentNum); // removes the opposite arrow direction

But if skip the above lines,it produces wrong output.Can u please explain this??

and one more thing..

boolean childHasChild = (grandChildren != null && !grandChildren.isEmpty());

here, I can't figure out the difference between the two conditions "grandChildren != null" and "!grandChildren.isEmpty()" both appear similiar to me but if I OR them instead of AND,obviously it produces wrong output...can you please explain them??

Thanks in advance!!