create a child from a nested symbol on the composition stage

it won't work.

If I I place the following code directly on a button which is on the main stage

everything works fine:

var videoholder = sym.createChildSymbol("videoholder", "Stage");

var move_videoholder = videoholder.getSymbolElement();

TweenMax.set(move_videoholder, {position:'absolute', left:10, top:500});

But If I put the code on a nested button it wont work. In my understanding,

I have to go back to the composition on the stage, but it wont work:

var videoholder = sym.getComposition().getStage().sym.createChildSymbol("videoholder", "Stage");

What did I do wrong?

Any healp would be great