[AS2]Levelling system help

guys im trying to make a level up system, for some reason when i reach required experience to level up, it will continuously increased my level
here my current code

var str:Number = 10;
var health:Number = 200;
var point:Number = 4;
var level:Number = 1;
var expe:Number = 0;
function onEnterFrame (){
if (_root.str <= 0){
    _root.str = 0;
}
if (_root.expe >= 20){
    level += 1;
    point += 4;
}
if (_root.expe >= 50){
    level += 1;
    point += 1;
}
}
stop ();

if you still didnt understand action speaks louder than word (i mean maybe you can look the file)