In this talk, I will present recent results on the cluster algebra structure of wavefunction coefficients in massless scalar theories in de Sitter cosmology. I will show that the symbol of the wavefunction coefficient associated with the n-site path graph P_n satisfies a natural generalisation of cluster adjacency: all letters appearing in a given word belong to a single cluster of the A_{2n-3} algebra. I will discuss the physical interpretation of this property and explain why it is stronger than the usual notion of cluster adjacency between neighbouring letters, imposing stronger constraints for the symbol bootstrap.
I will also describe how arbitrary tree graphs exhibit an analogous cluster-like structure encoded by tubes and tubings on the underlying graph, enabling a similar bootstrap strategy in the general case.