How to get the key of the first max value in a C# Dictionary?

Question

I want to get the keys of the highest values in a dictionary {'a' : 1, 'b' : 2, 'c' : 2}. In this case I want it to return 'b' but use of

weight.Aggregate((l, r) => l.Value > r.Value ? l : r).Key;

returns the last largest value i.e. 'c'.

1. Is there a way to return the key of the first largest value in my dictionary? =>'b'
2. Also, is it possible to return an array of keys of the max tied values? => new char[]{'b', 'c'}
3. Which Key-Value data structure should I use instead?

EDIT: Since it has caused quite a stir in the comments, I mean the first largest value in terms of insertion order.