Function insertion

Trees/binarytreetraversal.c:22–30

  void insertion(struct tnode **node, int data) {
        if (!*node) {
                *node = createNode(data);
        } else if (data < (*node)->data) {
                insertion(&(*node)->left, data);
        } else if (data > (*node)->data) {
                insertion(&(*node)->right, data);
        }
  }
  void postOrder(struct tnode *node) {
        if (node) {
                postOrder(node->left);