code: public static MutableTreeNode leftShift(MutableTreeNode self, MutableTreeNode node) {
          self.insert(node, self.getChildCount());
          return self;
      }
docs: Overloads the left shift operator to provide an easy way to add
  nodes to a MutableTreeNode.<p>
  
  @param self a MutableTreeNode
  @param node a node to be added to the treeNode.
  @return same treeNode, after the value was added to it.
  @since 1.6.4