No, you cannot. The card text on LV X cards specifically states on what card you can play the LV X, and none of those cards say that you play the LV X on top of another LV X. For example, Garchomp C LV X's card text reads as follows (the other LV X cards have similar text):
Put this card onto your Active Garchomp C. Garchomp C LV.X can use any attack, Poké-Power, or Poké-Body from its previous Level.
Furthermore, conceptually speaking, when a Pokemon is leveled up to LV X, it has reach the highest level possible. Therefore, it would be illogical to assume it could further be leveled up.
