Centering and adding a push button to a grid window, TKinter

[menator01]

I have one more example. Doesn't use the button to update. uses after. Sometimes pulls the same bin multiple times in the comparison list though.
So instead of three red labels, will get only one or two.

import tkinter as tk
from random import choices

aList = ["Bin 1", "Bin 2", "Bin 3", "Bin 4", "Bin 5","Bin 6", "Bin 7", "Bin 8", "Bin 9", "Bin 10", "Bin 11",
        "Bin 12", "Bin 13", "Bin 14", "Bin 15"]


def checker(root, labels):
    bins = choices(aList, k=3)
    print(bins)
    for label in labels:
        label['bg'] = 'red' if label['text'] in bins else 'gray86'
    root.after(1000, lambda: checker(root, labels))


root = tk.Tk()
root['padx'] = 5
root['pady'] = 5
root.title('Feed Bins')

root.columnconfigure(0, weight=1)
root.rowconfigure(0, weight=1)

frame = tk.Frame(root)
frame['highlightbackground'] = 'black'
frame['highlightcolor'] = 'black'
frame['highlightthickness'] = 1
frame.grid(column=0, row=0, sticky='news', padx=5, pady=5)

_labels = []
i = 0
for x in range(5):
    frame.grid_rowconfigure(x, weight=3, uniform='rows')
    for y in range(3):
        frame.grid_columnconfigure(y, weight=3, uniform='cols')
        _labels.append(tk.Label(frame, text=aList[x+(y*5)], relief='raised', font=(None, 16, 'bold')))
        _labels[i]['bg'] = 'gray86'
        _labels[i].grid(column=y, row=x, sticky='news', padx=5, pady=5)
        i+=1


btn = tk.Button(root, text='Button', font=(None, 14, 'bold'))
btn.grid(column=0, row=1, pady=8)
root.after(1000, lambda: checker(root, _labels))
root.mainloop()