Lists show up as System.Collection.Generic.List in C# button output

Hi.

Inside a C#-Script button am generating several Point lists I want to add them to a tree and use the in Grasshopper.

Code-snippets:

DataTree<List<Point3d>> output = new DataTree<List<Point3d>>();

// inside a for loop:

List<Point3d> curveA = new List<Point3d>();

List<Point3d> curveB = new List<Point3d>();

....  fill the lists ...

// add to tree

int[] branchPath = new int[2] {k, 0};
output.Add(curveA, new GH_Path(branchPath));
branchPath[1] = 1;
output.Add(curveB, new GH_Path(branchPath));

.....

Instead of giving me a tree I can work with, the tree contains 2 System.Collection.Generic.List .. which are not recognised in Grasshopper. The values are not reachable...

If I skip the tree and return only one list, it works fine...

Any thoughts?

Cheers from the Switch the LampiOn Workshop in Trier