Why is the tree constructed this way incorrect?

The result of decoding the tree constructed using the first write-up is correct, but the tree constructed using the second write-up is decoded incorrectly, why? I thought they were equivalent but they are not, and I can't figure out the problem within the second version :( To make things clear, here is the correct diagram of the tree I want to construct: Graph of the tree

Tree* buildTree() {
    Tree* root, * curr;
    root = getNode('0');//set irrelevant node value to be '0'
    curr = root->left = getNode('0');
    curr->left = getNode('b');
    curr->right = getNode('g');
    curr = root->right = getNode('0');
    curr->right = getNode('e');
    curr = curr->left = getNode('0');
    curr->right = getNode('0');
    curr->right->left = getNode('a');
    curr->right->right = getNode('h');
    curr = curr->left = getNode('0');
    curr->right = getNode('d');
    curr = curr->left = getNode('0');
    curr->left = getNode('c');
    curr->right = getNode('f');
    return root;

}

And here the second version(the wrong one)

Tree* buildTree() {
    Tree* root, * curr;
    root = getNode('0');//不是解码关键节点的点，值都设为‘0’,*100
    root->left =root->right = getNode('0');
    root->left->left = getNode('b');//19
    root->left->right = getNode('g');//21
    root->right->right = getNode('e');
    curr = root->right->left = getNode('0');
    curr->left = curr->right = getNode('0');
    curr->right->left = getNode('a');
    curr->right->right = getNode('h');
    curr = curr->left = getNode('0');
    curr->left = getNode('0');
    curr->right = getNode('d');
    curr->left->left = getNode('c');
    curr->left->right = getNode('f');
    return root;

}

I tried comparing the two write-ups one-to-one with the tree illustration and didn't find any difference, but it turns out that they construct different results for decoding the tree.

Solution

The problem is that when you construct the tree you reuse node when you shouldn't be. For example here:

root->left = root->right = getNode('0');

This is wrong because now left and right are the same node. And now when you set stuff on the node:

root->left->left = getNode('b');

Since root->left and root->right are the same, you also affected root->right

You might be confused by what the original code is doing here:

curr = root->left = getNode('0');

This means that curr points to the same node as root->left. Modifying curr also modify root->left.

To fix this problem, make sure you create a new node every time, e.g.

root->left = getNode('0');
root->right = getNode('0');