Button to create new items only toggles

Hi all,

Thanks for a great platform. I’m trying to create an app that allows the user to build a series of objects, basically as many as they want. I create a button to allow them to add another. However to my great surprise the button works to add a second item, and then toggles back to one rather than adding a third. Here is a MWE

import streamlit as st

class Builder:
	def __init__(self):
		st.header('Build tuple')
		self.button = st.empty()

	def build_multiple(self, multiple=(), level=0):
		single = self.build_one()

		if self.button.button('Build another', level):
			multiple = (single,) + self.build_multiple(multiple,level=level+1)
		return multiple

	def build_one(self):
		st.subheader('Building one')
		# Logic to build my items
		return "Hello"

builder = Builder()
items = builder.build_multiple()

What is going on here? Thanks in advance.