LASImportMenu.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;

public class LASImportMenu 
{
    [MenuItem("LAS/LAS Import", false, 0)]
    public static void Import()
    {
        string filename = EditorUtility.OpenFilePanel("Import LAS", "", "las");
        if (string.IsNullOrEmpty(filename) == false)
        {
            LASImporter importer = new LASImporter();
            importer.Import(filename);
        }
    }
}