ArcGIS 一级文件夹下所有GDB中的指定要素添加到mxd的图层中

一级文件夹下存在多个GDB，每个GDB存在多个要素类，要求对名字为frame的要素类，添加到mxd的图层中显示 如下图：

mxd = arcpy.mapping.MapDocument('CURRENT')
df = arcpy.mapping.ListDataFrames(mxd)[0]

arcpy.env.workspace = 'D:/.../一级文件夹'
wks = arcpy.ListWorkspaces(workspace_type="FileGDB")
for wk in wks:   
    arcpy.env.workspace = wk
    features = arcpy.ListFeatureClasses('frame') # 要加载全部要素，修改此处
    for f in features: 
        lyr = arcpy.mapping.Layer(f)
        arcpy.mapping.AddLayer(df,lyr)