Tree.Simple
val node : ?ls:Num.t -> ?cs:Num.t -> ?arrow_style:arrow_style -> ?edge_style:edge_style -> ?stroke:Color.t -> ?brush:Brush.t -> ?pen:Pen.t ->
?sep:Num.t -> ?valign:Command.position -> ?halign:Command.position -> Box.t -> t list -> t
a simple tree placement algorithm: align all subtrees horizontally , and place the parent node above. Default arrow_style is Directed
. Default edge_style is Straight
.