Dollar tree was not a dollar tree back then it was a toy store. It was a toy store call K and K toys. Also, the toys they selled were not only a dolor. The price was like normal prices like a toy could be $20 dollars.
This store called dollar tree sells food, toys,housewares and cleaning supplies. Also, they sell health and beauty aids, hardware, books, paper products and other things. you might think that you are going to spend a lot of money but every thing is one dollar. The reason that every thing is a dollar is because they buy things in huge quantities to get a discount on the products.
The first article said that family dollar and dollar tree are going to come together to make more money and so they don't have to compete with each other. Source: The New York Times
The second article said that the stock is 10% higher. This affects dollar tree because it will get more people to buy the stock or will come and buy things at the store. Source: fool.com