Generic tree constructor

package com.company;

import java.util.ArrayList;
import java.util.Stack;

public class constructorr {
    public static void main(String[] args) {
        Node root;
        int arr[] = {10, 20, 50, -1, 60, -1, -1, 30, 70, -1, 80, 110, -1, 120, -1, -1, 90, -1, -1, 40, 100, -1, -1, -1};
        Stack<Node> st = new Stack<>();

        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == -1) {
                st.pop();
            } else {
                Node t = new Node();
                t.data = arr[i];
                if (st.size() > 0) {
                    st.peek().children.add(t);

                } else {
                    root = t;
                }
                st.push(t);
            }
        }
    }
        private class Node {
            int data;
            ArrayList<Node> children = new ArrayList<>();
        }
    }