The tree in this video รจ is 210 cm (6.9 ft) tall and has been decorated with only one Twinkly, for a total of 100 LED lights, all of them placed on one visible side.

The answer depends on your taste, on the positioning of your tree (how many sides is visible from) and on the density you want to obtain.

Remember that it is possible to use together more Twinkly on the same tree, see It is possible to join 2 or more Twinkly?