An end-user rendering system including an advertisement database to receive advertisements, and store the advertisements therein, a state database to store information, a decision model optimization module to receive a tree-type decision model and optimize the tree-type decision model based on at least some of the information stored in the state database, an advertisement decision module to evaluate the optimized tree-type decision model and select an advertising campaign, the selected advertising campaign having at least one advertisement, and a rendering module to render the at least one advertisement of the selected advertising campaign. Related apparatus and methods are also described.