public void inOrder(Node root){
        if(root == null){
            return;
        }
        inOrder(root.left);
        System.out.print(root.data + " ");
        inOrder(root.right);
    }
Youtube link - https://youtu.be/nzmtCFNae9k
Youtube link - https://youtu.be/elQcrJrfObg
Youtube link - https://youtu.be/qT65HltK2uE
Youtube link - https://youtu.be/ZM-sV9zQPEs

http://www.geeksforgeeks.org/inorder-tree-traversal-without-recursion/
http://www.geeksforgeeks.org/inorder-tree-traversal-without-recursion-and-without-stack/
http://www.geeksforgeeks.org/iterative-preorder-traversal/
src/com/interview/tree/TreeTraversals.java