Code problem, display in client not working

import java.util.ArrayList;
import java.util.Scanner;

public class GT_Construction {

	 class Node {
		int data;
		ArrayList<Node> children;

		Node(int data) {
			this.data = data;
			this.children = new ArrayList<>();

		
	}
	 private Node root;
	 private int size;
     void GT_Construction() {
        Scanner scn=new Scanner(System.in);
		this.root=takeInput(scn,null,0);
		
	}
	Node takeInput(Scanner scn,Node parent,int ith_child) {
		if(this.root==null) {
			System.out.print("Enter the data for the root node");
		}
		else {
			System.out.print("Enter the data for its"+ith_child+"ith_child of"+parent.data);
		}
		int nodeData=scn.nextInt();
		Node node =new Node(nodeData);
		this.size++;
		System.out.print("Enter the number of children for"+node.data);
		int children=scn.nextInt();
		for(int i=0;i<children;i++) {
			Node child=this.takeInput(scn,node,i);
			node.children.add(child);
		}
		
		return node;

}
	public void display() {
		this.display(this.root);
	}
	private void display(Node node) {
		String str=node.data+"=>";
		for(int i=0;i<node.children.size();i++) {
			str=str+node.children.get(i).data+",";
		}
		str=str+"END";
		System.out.println(str);
		for(int i=0;i<node.children.size();i++) {
			this.display(node.children.get(i));
		}
	}

	 }

}