`include S with type Tree.V.label = DGraphModel.DotG.V.t`
`module Tree : Graphviz.GraphWithDotAttrs with type V.label = DGraphModel.DotG.V.t`
`module TreeManipulation : sig ... end`
`type cluster = string`
`type graph_layout`
`class tree_model : graph_layout -> TreeManipulation.t -> [Tree.V.t, Tree.E.t, cluster] Graph__.DGraphModel.abstract_model`
`val tree : unit -> TreeManipulation.t`
`val from_model : ?depth_forward:int -> ?depth_backward:int -> DGraphModel.dotg_model -> DGraphModel.DotG.V.t -> tree_model`