dot D:\test\1.gv -Tpng -o image.png

graph pic1 { 
 a -- b
 a -- b
 b -- a [color=blue]
} 

digraph pic2 { 
 a -> b
 a -> b
 b -> a [style=filled color=blue]
}

digraph startgame {
  label="游戏资源更新流程"
  rankdir="TB"
  start[label="启动游戏" shape=circle style=filled]
  ifwifi[label="网络环境判断是否 WIFI" shape=diamond]
  needupdate[label="是否有资源需要更新" shape=diamond]
  startslientdl[label="静默下载" shape=box]
  enterhall[label="进入游戏大厅" shape=box]

  enterroom[label="进入房间" shape=box]
  resourceuptodate[label="资源不完整" shape=diamond]
  startplay[label="正常游戏" shape=circle fillcolor=blue]
  warning[label="提醒玩家是否更新" shape=diamond]
  startdl[label="进入下载界面" shape=box]
  //{rank=same; needupdate, enterhall}

  {shape=diamond; ifwifi, needupdate}

  start -> ifwifi
  ifwifi->needupdate[label="是"]
  ifwifi->enterhall[label="否"]
  needupdate->startslientdl[label="是"]
  startslientdl->enterhall
  needupdate->enterhall[label="否"]

  enterhall -> enterroom
  enterroom -> resourceuptodate
  resourceuptodate -> warning[label="是"]
  resourceuptodate -> startplay[label="否"]
  warning -> startdl[label="确认下载"]
  warning -> enterhall[label="取消下载"]
  startdl -> enterhall[label="取消下载"]
  startdl -> startplay[label="下载完成"]
}

from sklearn.tree import export_graphviz  # 导入的是一个函数
# tree表示已经训练好的模型，即已经调用过DecisionTreeClassifier实例的fit(X_train, y_train)方法
export_graphviz(tree, out_file='tree.dot', 
    feature_names=['petal length', 'petal width'])

dot -Tpng tree.dot -o tree.png