while(curr) {        //print left most node, notice the root node        if ((curr->left && curr->left->visited == false) || (curr->right && curr->right->visited == false)) {            while (curr->left || curr->right) {                if (curr->left && curr->left->visited == false) {                    curr = curr->left;                    treeStack.push_back(curr);                    continue;                }                curr = curr->right;                treeStack.push_back();            }            continue;        }        printTree(curr);        curr->visited = true;        curr = treeStack.pop_back();    }