The aim of the article is to give a conceptual understanding of Kontsevich’s construction of the universal element of the cohomology of the coarse moduli space of smooth algebraic curves with given genus and punctures. In a first step the author presents a toy model of tree graphs coloured by an operad $𝒫$ for which the graph complex and the universal cycle will be constructed. The universal cycle has coefficients in the operad for $\Omega \left({𝒫}^{*}\right)$-algebras with trivial differential over the (dual) cobar construction...