There are some great tutorials about this kind of thing. I recommend you check out some of those to get a structure to start your game.
That might have been a slight typo - I think you want add_child not add_tree.
To call this you need a new Node, and you call it from the Node which you want to be the Parent. You can create a new Node from your scene file using instance().
Here is example code (this might have some typos)
var Player = preload("res://TopPlayer/TopPlayer1.tscn")
var newplayer = Player.instance()
# do things to setup your new player instance here, for example position
newplayer.position = Vector2(rand_range(0,500),rand_range(0,500))