Here's why:
* Cut is a move, not an item. Cut is a move that some Pokemon learn, like Scyther. You can't use it as an item like you can use a Poke Ball or Potion.
* Team Rocket doesn't block paths with trees. In Heart Gold, Team Rocket doesn't use trees to block your path. They typically use their own Pokemon or traps to stop you.
Let me know if you have any other questions about Pokemon Heart Gold!