layer_tree Grasshopper Python script

gistfile1.py

import Rhino
import scriptcontext
import System.Collections.Generic as SCG


# for accesssing GH classes
import clr
clr.AddReference("Grasshopper")
from Grasshopper.Kernel.Data import GH_Path
from Grasshopper import DataTree


layerTree = DataTree[SCG.IEnumerable[Rhino.Geometry.GeometryBase]]() # make a DataTree
for i in range(len(layernames)):
    objs = scriptcontext.doc.Objects.FindByLayer(layernames[i])
    geoms = [obj.Geometry for obj in objs]
    path = GH_Path(i)
    layerTree.Add(geoms, path)
a = layerTree