These lights allow you to create custom displays on your tree, you can add to existing setups if you have some Twinkly lights already or try them out, you won't be disappointed. They come with a number of effects built in but to get the most out of the lights you need to download the Twinkly app which allows you to map the lights and download new light effects. These are the gen II lights which have bluetooth for easier setup and can support larger displays with up to 10 individual lights combined into a single contiguous display.
There are 250 lights on two 10m lengths for a total of 20m, this is enough for a tree of around 5ft.