c – Unival Tree Implementation

I have written some code to solve the following interview question. Please advise how it can be improved. Thanks in advance.

A unival tree (which stands for “universal value”) is a tree where all nodes under it have the same value. Given the root to a binary tree, count the number of unival subtrees.
For example, the following tree has 5 unival subtrees:

Unival Tree

Implementation:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

typedef struct stTree
{
    struct stTree * left;
    struct stTree * right;
    int value;
}

stTree;

stTree* createNode(int value)
{
    stTree *node = malloc(sizeof *node);
    node->left = NULL;
    node->right = NULL;
    node->value = value;

    return node;
}

bool isTreeUniv(stTree *node)
{
    bool flag = true;

    if (!node)
        return false;

    if (node->right && node->right->value != node->value)
    {
        flag = false;
    }

    if (node->left && node->left->value != node->value)
    {
        flag = false;
    }

    return flag;
}

stTree* insertRight(stTree *currNode, int value)
{
    stTree *node = malloc(sizeof *node);

    currNode->right = node;
    node->left = NULL;
    node->right = NULL;
    node->value = value;
    return node;
}

stTree* insertLeft(stTree *currNode, int value)
{
    stTree *node = malloc(sizeof *node);

    currNode->left = node;
    node->left = NULL;
    node->right = NULL;
    node->value = value;
    return node;
}

unsigned int uTreeCount = 0;
void countUnivSubT(stTree *Node)
{
    if (isTreeUniv(Node))
        uTreeCount++;

    if (Node->left)
        countUnivSubT(Node->left);

    if (Node->right)
        countUnivSubT(Node->right);

}

int main(void)
{
    //build a tree
    stTree *rootNode = createNode(0);
    insertLeft(rootNode, 1);
    insertRight(rootNode, 0);

    insertLeft(rootNode->right, 1);
    insertRight(rootNode->right, 0);

    insertLeft(rootNode->right->left, 1);
    insertRight(rootNode->right->left, 1);

    countUnivSubT(rootNode);
    printf("total universal subree: %un", uTreeCount);

}