TriggerEditor.cs

using UnityEngine;
using UnityEditor;

[CustomEditor (typeof(Trigger))]
[CanEditMultipleObjects()]
public class TriggerEditor : Editor
{
    private SerializedObject obj;
    private SerializedProperty radius;

    public void OnEnable()
    {
        obj = new SerializedObject(target);
        radius = obj.FindProperty("radius");
    } 

    public override void OnInspectorGUI()
    {
        obj.Update();
        GUIStyle style = new GUIStyle();
	style.font = EditorStyles.boldFont;
        EditorGUILayout.LabelField("Trigger", style, null);
        EditorGUILayout.PropertyField(radius);
		
        obj.ApplyModifiedProperties(); 
    }
    
    public void OnSceneGUI()
    {
        // Implement what you want to see in scene view here
    }
}