Scrolls the tree view such that the top-left corner of the visible area is
tree_y are specified in tree coordinates.
The this must be realized before this function is called. If it isn't, you probably want to be using scroll_to_cell.
tree_y are -1, then that direction isn’t scrolled.
X coordinate of new top-left pixel of visible area, or -1
Y coordinate of new top-left pixel of visible area, or -1