Program to check if a binary tree is height balanced or not

package com.company;

import java.io.*;
import java.lang.*;
import java.util.*;

public class Main {
public static void main(String[] args) {
abc tree =new abc();
tree.add(8);
tree.add(5);
tree.add(9);

System.out.println(tree.isbalanced(tree.root));
}
}
class node {
int data;
node left;
node right;

public node(int data) {
this.data = data;
this.left=null;
this.right=null;
}
}
class abc{
public node root=null;
public node insert(node node ,int value){
if (node==null){
return new node(value);
}
else if (valuenode.data){
node.right=insert(node.right,value);
}
return node;
}
public void add(int value){
root =insert(root,value);
}
public boolean isbalanced(node node ){
if (node==null){
return true;
}
int lh =height(node.left);
int rh =height(node.right);
if (Math.abs(lh-rh)<=1&&isbalanced(node.left)&&isbalanced(node.right)){
return true;
}
else {
return false;
}

}
static int height(node node){
if (node==null){
return 0;
}
else {
return 1+Math.max(height(node.left),height(node.right));
}
}
}