set button background with image of window background

[gray]

hello freinds
i have put an image (self.image) on my window background 
 now,
i need to put another image(mi_but1) on this window..
my problem:
image mi_but1 is put on window with a gray square behind it(a gray square between image mi_but1 and window's background) 
see the attached file...it doesnt look nice
i don't want this gray background...
what should I do? how can i remove this gray square behind the button(button background)? OR how can i put the image of window background(self.image) in behind of the button (button background)
my code:

from tkinter import *
from PIL import Image, ImageTk

root = Tk()
root.title("Title")
root.geometry("400x400")
root.configure(background="black")

class Example(Frame):
    def __init__(self, master, *pargs):
        Frame.__init__(self, master, *pargs)

        self.image = Image.open("/home/pi/Desktop/images/background/image.png")
        self.img_copy= self.image.copy()


        self.background_image = ImageTk.PhotoImage(self.image)

        self.background = Label(self, image=self.background_image)
        self.background.pack(fill=BOTH, expand=YES)
        self.background.bind('<Configure>', self._resize_image)

        mi_but1=PhotoImage(file="/home/pi/Downloads/images/buttons/starlarg.png")
        button2 = Button(self.background, text='button2',image=mi_but1)
        button2.image=mi_but1
        button2.pack(side='top')

    def _resize_image(self,event):

        new_width = event.width
        new_height = event.height

        self.image = self.img_copy.resize((new_width, new_height))

        self.background_image = ImageTk.PhotoImage(self.image)
        self.background.configure(image =  self.background_image)

e = Example(root)
e.pack(fill=BOTH, expand=YES)
root.mainloop()