Where does my Huffman encoding method go wrong?

I am trying to code a Huffman string encoding algorithm.

My solution works this way:

1. since every letter in the string have a special binary code associated to it, search the binary tree and when a letter is found, add it to the map with binary code. (where I went wrong is here)
2. iterate on the string, and for each letter, associate the value associated with the key of the letter of the map.

I don't have the tree printed somewhere, even tough it could help you help me, but here is what I get for the string abracadabra, and what I should get:

Correct Code : 000010000110110101111101011000111110110100111011101100101101110000110000110111100101111101010010

What I get : 00001000111011010110101111010101100011101011010

Here is my code:

#include <algorithm>
#include <map>

string codes = "";

void getMapCharBinaryCode(Node root, string &prefix, map <char, string> &m){
    if(!root) return;
    if(root->value){
        if(!m.count(root->value)){
            m[root->value] = prefix;
            prefix = "";
        } 
    }
    if(root->leftChild){
        getMapCharBinaryCode(root->leftChild, prefix += "0",m);
    }
    if(root->rightChild){
        getMapCharBinaryCode(root->rightChild, prefix += "1",m);
    }
   
}

string encode(string text, Node tree){
    // text is "abracadabra"
    // create map for each char -> binary code
    map<char, string> m;
    string prefix = "";
    getMapCharBinaryCode(tree, prefix, m);
    
    // iterate on text and assign each letter with binary code from map
    for(int i = 0; i < text.size(); i++) {
        codes += m[text[i]];
    }
    return codes;
}