How do i make the treee white and the background black

Use Select>Color range to select all the white areas (click with the eye dropper anywhere in the white area), use a high value for Fuzzyness (175 or so). Then fill the selection with black (Shift+Delete, select Fill with Black). Then invert the selection and fill with white. To refine the image, paint with White over the white tree using a soft brush in Vivid Light mode, low flow (8% or so). Then switch the color to black and paint over the black areas.