class_docstr: xml filter that insert a subplot
docstr: Apply the filter on the tree
docstr_tok: ["Apply","the","filter","on","the","tree"]
code: def __call__(self, T):
      """Apply the filter on the tree"""
      subplot = Bar(
          legend_at_bottom=True,
          explicit_size=True,
          width=800,
          height=150,
      )
      subplot.add("Difference", self.data)
      subplot = subplot.render_tree()
      subplot = subplot.findall("g")[0]
      T.insert(2, subplot)
      T.findall("g")[1].set(
          "transform", "translate(0,150), scale(1,0.75)"
      )
      return T
  
imports: from pygal import Bar
label_desc: Use image node_id 2 for calling the ChangeBarsXMLFilter obj's underlying member method code with example usage: obj.__call__(T) and returns: T