Why would pressing the play button delete or recreate a list elements?

I have MonoBehaviour with two lists for nodes and edges. Edge has links to nodes witch is ends of this. When i am creating edge it works currectly, but when i am pressing play button edge already has links to another copies of nodes... and it's all. So how can i fix it?

Edge class:

 using System;
 using UnityEngine;
 
 [Serializable]
 public class Edge {
 
     public Node[] nodes = new Node[2];
 }

Node class:

 using System;
 using UnityEngine;
 
 [Serializable]
 public class Node
 {
     public Vector3 position;
 }

Graph class:

 using System.Collections.Generic;
 using UnityEngine;
 
 public class Graph : MonoBehaviour {
 
     public List<Node> nodes;
     public List<Edge> edges;
 }
 

GraphEditor class:

 using UnityEditor;
 using UnityEngine;
 
 [CustomEditor(typeof(Graph))]
 public class GraphEditor : Editor {
 
     Graph graph;
 
     private Node selectedNode;
     private Node connectedNode;
 
     private float handleSize = 0.1f;
     private float pickSize = 0.1f;
 
     private void OnEnable()
     {
         selectedNode = null;
         graph = (Graph)target;
     }
 
     private void OnSceneGUI()
     {
         var transform = graph.transform;
 
         for (int i = 0; i < graph.edges.Count; i++)
         {
             var edge = graph.edges[i];
             Handles.DrawLine(transform.TransformPoint(edge.nodes[0].position), transform.TransformPoint(edge.nodes[1].position));
         }
 
         for (int i = 0; i < graph.nodes.Count; i++)
         {
             var node = graph.nodes[i];
 
             var point = transform.TransformPoint(node.position);
             if (Handles.Button(point, Quaternion.identity, handleSize, pickSize, Handles.DotHandleCap))
             {
                 selectedNode = node;
 
                 if (connectedNode != null)
                 {
                     var edge = new Edge { nodes = new Node[] { selectedNode, connectedNode } };
                     graph.edges.Add(edge);
 
                     connectedNode = null;
                 }
             }
 
             if (selectedNode == node)
             {
                 EditorGUI.BeginChangeCheck();
                 point = Handles.DoPositionHandle(point, Quaternion.identity);
                 if (EditorGUI.EndChangeCheck())
                 {
                     Undo.RecordObject(graph, "Move Node");
                     node.position = transform.InverseTransformPoint(point);
                     EditorUtility.SetDirty(graph);
                 }
             }
         }
     }
 
     public override void OnInspectorGUI()
     {
         base.OnInspectorGUI();
         if (GUILayout.Button("Connect Nodes"))
         {
             Undo.RecordObject(graph, "Connect Nodes");
             EditorUtility.SetDirty(graph);
             connectedNode = selectedNode;
         }
     }
 }

Before play: After: