Is there a way for case objects to have cases share fields?

[treeform]

I want both nkDocument and nkCanvas to have children, but not nkRectangle? Is 
there a way to do this?
    
    
    type
      NodeKind = enum
        nkDocument
        nkCanvas
        nkRectangle
      
      Node = ref object
        case kind: NodeKind
        of nkDocument:
          children: seq[Node]
        of nkCanvas:
          children: seq[Node]
        of nkRectangle:
          box: Rect
    
    
    Run