code: public void preserveParseTree(String name) {
          if (mPreserveTree == null) {
              mPreserveTree = new HashSet<String>();
          }
          mPreserveTree.add(name);
      }
docs: After a template is compiled, all but the root node of its parse tree
  is clipped, in order to save memory. Applications that wish to traverse
  CompilationUnit parse trees should call this method to preserve them.
  This method must be called prior to compilation and prior to requesting
  a parse tree from a CompilationUnit.
  
  @param name fully qualified name of template whose parse tree is to be
  preserved.