像这样的吗

var list = myDico.Select(x => new Tuple<long, int>(x.Key, x.Value)).ToList();

你可以试试这个

var applyOnTree = myDico.Select(x => Tuple.Create(x.Key, x.Value)).ToList();

在隐式元组的情况下：

IList<(long First, int Second)> applyOnTree;

applyOnTree = myDico
   .Select(x => (
      First: x.Key, 
      Second: x.Value))
   .ToList();