My intention is to create gui from several classes and as exercise I created small example. As can be seen in app self.greet should be button created from class Button, but what I get is generic button (without text and callback function). 
Any suggestions?

```
import tkinter as tk
import tkinter.ttk as ttk

class Button(ttk.Button):

    def __init__(self, parent):
        super().__init__(parent)

        self.item = ttk.Button(parent, text="Greet", command=self.greet)

    def greet(self):
        print("Greetings!")

class App():

    def __init__(self, parent):        
        parent.title("A simple GUI")

        self.label = ttk.Label(parent, text="A label")
        self.greet = Button(parent)
        self.button = ttk.Button(parent, text="Close", command=parent.quit)

        self.label.grid(row=0, column=0, sticky=(tk.N, tk.S, tk.W, tk.E))
        self.greet.grid(row=1, column=0, sticky=(tk.N, tk.S, tk.W, tk.E))
        self.button.grid(row=2, column=0, sticky=(tk.N, tk.S, tk.W, tk.E))

        parent.grid_columnconfigure(0, weight=1)        

    def greet(self):
        print("Greetings!")

if __name__ == "__main__":
    root = tk.Tk()
    app = App(root)
    root.mainloop()

```