bassackwards prefix parser.cs

void Main()
{
  var rootList = new List<Node>(new[]{ new Node() });  // only ever one root, I assume.
  var childrenAtThisLevel = FillLevel(rootList);
  while(childrenAtThisLevel.Count > 0)
    childrenAtThisLevel = FillLevel(childrenAtThisLevel);
}

List<Node> FillLevel(List<Node> childrenAtThisLevel)
{
  var childrenAtNextLevel = new List<Node>();
  foreach(var child in childrenAtThisLevel)
  {
    child.Label = GetNextSymbol();
    var newChildCount = GetNumberOfChildrenForThisSymbolType(child.Label)  // 0 1 or 2
    for(var i=0; i<newChildCount; i++)
    {
      var newChild = new Node();
      child.Children.Add(newNode);
      childrenAtNextLevel.Add(newChild);
    }
  }
}