function OnGUI () {
    GUILayout.BeginVertical();
    GUILayout.Button("Short Button", GUILayout.ExpandWidth(false));
    GUILayout.Button("Very very long Button");
    GUILayout.EndVertical();
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnGUI() {
        GUILayout.BeginVertical();
        GUILayout.Button("Short Button", GUILayout.ExpandWidth(false));
        GUILayout.Button("Very very long Button");
        GUILayout.EndVertical();
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnGUI():
        GUILayout.BeginVertical()
        GUILayout.Button('Short Button', GUILayout.ExpandWidth(false))
        GUILayout.Button('Very very long Button')
        GUILayout.EndVertical()