.Append not working

Hello,

I have the following code:

//make a list of all BUYs
allBuys = Positions.Where(p => p.TradeType == TradeType.Buy);

//get the BUY with the highest price
var last_in = allBuys.OrderByDescending(x => x.EntryPrice).First();

//make another list of positions
var buyBundle = new[] { last_in };

//when I try this, nothing is added to buyBundle
var to_add = allBuys.OrderByDescending(x => x.EntryPrice).Last();
buyBundle.Append(to_add);

Is there something wrong with the declaration of buyBundle? Or where is the error? The compiler doesn't throw any errors.

Thank you,
Dinu