class Tree {
public:
    std::string value;
    std::vector<Tree> tree;
};

1+2*3

[+]-|
    |-[1]
    |
    |-[*]-|
    |     |-[2]
    |     |-[3]

#include <iostream>
#include <string>
#include <vector>

class Tree {
public:
    std::string value;
    std::vector<Tree> tree;
};

void printTree (Tree tree, int offsetWidth = 0, std::string offsetStr = "") {
    std::string str = "[" + tree.value + "]";
    std::string offset(offsetWidth + 1, ' '); // +1 because of '-' character on line 19
    offset = offset.replace(0, offsetStr.length(), offsetStr);
    int length = str.length();
    int size = tree.tree.size();
    if (offsetWidth > 0) {
        offset += "|";
        std::cout << offset << "-";
    }
    std::cout << str;
    if (size > 0) {
        std::cout << "-|\n";
        for (int i = 0; i < size; i++) {
            if (offsetWidth > 0) {
                printTree(tree.tree[i], length + offsetWidth + 3, offset); // +3 because of '[', ']', '-' characters
            }
            else {
                printTree(tree.tree[i], length + offsetWidth, offset);
            }
            if (i == size - 1) {
                std::cout << offset;
                std::cout << "\n";
            }
        }
    }
    else {
        std::cout << "\n";
    }
}

int main (int argc, char* argv[]) {
    print(tree);
    std::cin.get();
    return 0;
}