public int countLeftNodes() {
    return countLeftNodes( overallRoot );
}
private int countLeftNodes( IntTreeNode root ) {
    // if no child nodes to check
    if( root == null ) {
        return 0;
    }
    // if left is present: add 1 to count, check left node, check sibling
    if( root.left != null ) {
        return 1 + countLeftNodes( root.left ) + countLeftNodes( root.right );
    }
    // if no left child node, check the right
    return countLeftNodes( root.right );
}