Changed data through EditorWindow isn't persistent.

Hello,

I am using a custom script to show an EditorWindow which will display the data of one script attached to GameObjects.

 using UnityEngine;
 using UnityEditor;
 using System.Collections;
 
 public class ShowLevelData : EditorWindow {
 
     private GameObject go;
     private Level level;
     // Add menu named "My Window" to the Window menu
     [MenuItem ("Window/Show Level Data")]
     static void Init () {
         // Get existing open window or if none, make a new one:
         ShowLevelData window = (ShowLevelData)EditorWindow.GetWindow (typeof (ShowLevelData));
         window.position = new Rect(150,150,113,149);
         window.minSize = new Vector2(113,149);
         window.ShowPopup();
     }
 
     void OnSelectionChange(){
         go = Selection.activeGameObject;
         level = go.GetComponent<Level>();
         Repaint();
     }
 
     void OnGUI () {
         if(level){
             level.level = EditorGUILayout.IntField("Level Number",level.level);
             EditorGUILayout.BeginVertical ();
             EditorGUILayout.LabelField("1  2  3  4  5  6  7");
             for(int i = 0;i<7;i++)
             {
                 EditorGUILayout.BeginHorizontal();
                 for(int j=0;j<7;j++)
                 {
                     level.levelData[i,j] = EditorGUILayout.Toggle (level.levelData[i,j]);
                 }
                 EditorGUILayout.LabelField(""+i);
                 EditorGUILayout.EndHorizontal();
             }
             EditorGUILayout.EndVertical();
         }
     }
 }
 

This script shows a two-dimensional array in my other script 'Level' attached to a GameObject in my scene. There are multiple objects with this script attached to them. So whenever I select them and have this window open, I can see the two dimensional array.

The changes I make to this is present as far as I don't close Unity. Once I close Unity and restart, its gone. Same is for any other property of the script I change,(for example, the level number).

I can see it updated in the inspector once I change it, but even if I save the scene, the changes don't stay if I close Unity.

Does any one know how to fix this?