如何在data.tree中绘制直边决策树？

Question

我根据data.tree建议的几个功能实现了这个library(data.tree) library(yaml) library(DiagrammeR) node=as.Node(yaml.load(" name: Plaintiff to Litigate? type: decision Litigate: type: chance Prove negligence, Win Case: type: chance p: 0.60 High damages: type: terminal p: 0.30 payoff: 2900000 Medium damages: type: terminal p: 0.40 payoff: 1900000 Low damages: type: terminal p: 0.30 payoff: 900000 Fail to prove negligence: type: terminal p: 0.40 payoff: -100000 Settlement Offer: type: terminal payoff: 1000000")) GetPrelimNodeLabel = function(node) switch(node$type, terminal = format(node$payoff, scientific = FALSE, big.mark = ","),'') GetEdgeLabel = function(node) { if (isNotRoot(node) && node$parent$type == 'chance') { label = paste0(node$name, " (", node$p, ")") } else { label = node$name } return (label) } GetNodeShape = function(node) switch(node$type, decision = "box", chance = "circle", terminal = "none") GetArrowHead = function(node) switch(node$type, terminal = "oinv", "none") SetEdgeStyle(node, fontname = 'helvetica', label = GetEdgeLabel, arrowhead=GetArrowHead) SetNodeStyle(node, fontname = 'helvetica', label = GetPrelimNodeLabel, shape = GetNodeShape) ToDiagrammeRGraph(node,direction = "climb") %>% set_global_graph_attrs("layout", "dot", "graph") %>% add_global_graph_attrs("rankdir", "LR","graph") %>% render_graph() 包，建议用于post的决策分析。

接下来，我想制作好看的树，如下所示：

但我能得到的就是这一个：

如何画出如上所示的直边？不过，我不介意这种颜色。

这是我的代码：

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