def add_horizontal(node)
      if(node.char > @char)
        if (@right === nil)
          @right = node
        else
          @right.add_horizontal(node)
        end
      else
        if (@left === nil)
          @left = node
        else
          @left.add_horizontal(node)
        end
      end
    end
def add_horizontal(node)
      if(node.char > @char)
        if (@right === nil)
          @right = node
        else
          @right.add_horizontal(node)
        end
      else
        if (@left === nil)
          @left = node
        else
          @left.add_horizontal(node)
        end
      end
    end
Create a new Node with the given char and optionally, parent node and value
 Add another node horizontally
 (within the left-right binary tree of this Node)