A step-by-step guide to creating a tree made almost entirely from maths, with plenty of examples. Alongside following simple instructions for making the trees, there is also the opportunity for pupils to create their own algorithms and discuss (in everyday language) how probability affects the appearance of their trees. The activity introduces pupils to the language of fractals: bifurcation; initiator; generator; self-similarity and so on. There is also a discussion on the use of random numbers by scientists in nature-modelling, in models of everything from avalanches to water boiling in a kettle. There are two sets of instructions for the fractal trees: Basic and Harder. Most of an upper KS2 class should be able to cope with the Harder tree. Use the Basic tree as a backup plan.