Christmas tree spiral

I'm trying to edit an expression which makes a perfect 3D Xmas tree spiral which a particle generator then follows.

I know this subject has come up before and I have tried to use some tips from this thread

http://forums.creativecow.net/thread/227/12276

However nothing looks as good as my first attempt.

So the current expression begins at the top of tree and builds outwards and downwards.

I need the expression to start at the bottom and build upwards and inwards.

Original Expression:

radius=-time*30
angle=-time*300;
x=radius*Math.cos(degreesToRadians(angle));
y=radius*Math.sin(degreesToRadians(angle));
z=time*50
center=[190,400,100];
add(center,[x,y,z]);


Any help/point in the right direction would be greatly appreciated.

That's it!

I'm very grateful for your help Dan.