请问这段代码怎么运行不了啊？

<p>import turtle<br >&gt;&gt;&gt; def tree(plist,l,a,f):<br >&nbsp;if l&gt;5:<br >&nbsp;&nbsp;lst=[]<br >&nbsp;&nbsp;for p in plist:<br >&nbsp;&nbsp;&nbsp;p.forward(1)<br >&nbsp;&nbsp;&nbsp;q=p.clone()<br >&nbsp;&nbsp;&nbsp;p.left(a)<br >&nbsp;&nbsp;&nbsp;q.right(a)<br >&nbsp;&nbsp;&nbsp;lst.append(p)<br >&nbsp;&nbsp;&nbsp;lst.append(q)<br >&nbsp;&nbsp;tree(lst,1*f,a,f)</p><p>def main():<br >&nbsp;p=turtle()<br >&nbsp;p.color(&quot;green&quot;)<br >&nbsp;p.pensize(5)<br >&nbsp;p.hideturtle()<br >&nbsp;p.getscreen().tracer(30,0)<br >&nbsp;p.left(90)<br >&nbsp;p.penup()<br >&nbsp;p.goto(x,y)<br >&nbsp;p.pendown()<br >&nbsp;t=tree([p],110,65,0.6375)</p><p><br ></p><p>main()</p><p></p><p><br ></p><p>显示错误：Traceback (most recent call last):<br >&nbsp; File &quot;&lt;pyshell#50&gt;&quot;, line 1, in &lt;module&gt;<br >&nbsp;&nbsp;&nbsp; main()<br >&nbsp; File &quot;&lt;pyshell#49&gt;&quot;, line 2, in main<br >&nbsp;&nbsp;&nbsp; p=Turtle()<br >NameError: name 'Turtle' is not defined</p>