Small example fix

examples/ex4.py

@@ -88,4 +88,4 @@ nminus1Hists.Do('Write')
 out.Close()
 
 # NOTE: Can plot full node to tree to ensure selections were made accurately (requires graphviz python package and Graphviz installation)
-a.PrintNodeTree('ex4_tree')
\ No newline at end of file
+a.PrintNodeTree('ex4_tree.png')
\ No newline at end of file

examples/ex5.py

@@ -74,4 +74,4 @@ a.MakeWeightCols()
 templateGroup = a.MakeTemplateHistos(ROOT.TH1F('mtt','m_{tt}',30,500,3500), 'invariantMass')
 
 a.DrawTemplates(templateGroup,'test_templates/')
-a.PrintNodeTree('ex5_tree',verbose=True)
+a.PrintNodeTree('ex5_tree.png',verbose=True)