To Kill A Mocking Bird Ch. 4-6

After reading these chapter you start to expect that Boo Radley is alive from Scout's conversations with the neighbor across the street and from when Scout ended up rolling into the Radley's front yard and heard laughter coming from inside the house. I found it odd that Scout found gum in the tree near the Radley's and then Jem and her found money in it the next day. It seems like someone was leaving things in the tree for Jem and Scout and I am wondering if so who and if not why is someone hiding things in the tree. I was also confused at the end of chapter 6 when it describes someone in a white shirt across the fence when Jem went to get his pants back. Who was that? It kinda ended the chapter in confusion for me.