Help fading in an object

I have a button with property _alpha set to 0 so it is invisble at the start of the movie, after my first elements have loaded, I want this button to appear in smoothly.

I have tried different code but can’t seem to get it right… if someone could help me to figure this out I will appreciate it.

What I’ve done so far is telling the movie at the end of my first tweening to bring the alpha property of my button to 100. But I want a smooth fade in…

any advice on how to write the code on that?