The Standard Model of Particles is describing all (or almost all) of our knowledge in the field of particle physics. Also, it is predicting processes and their properties, such as cross sections, with great precision that is in agreement with the experiment. But the Standard Model is incomplete as a theory because there are still parts of physics that are not covered by it such as gravity or dark matter. One of the simple possible ways to extend the Standard Model is found in its Higgs sector. In the Standard Model, the solution that achieves the Higgs mechanism, crucial for obtaining the masses of particles, is the simplest possible. However, nothing prevents the existence of a more complex solution. One such solution is in the form of two additional scalar fields in the Higgs sector, which predicts the existence of two new scalar particles, X and Y. Those particles, in the mass regime MX > MY + MH and MY > 2MH, can decay into 3 Higgs bosons in X → Y H → HHH cascade. Although in the Standard Model there is a possibility of producing 3 Higgs bosons in a collision, the expected cross-section for that process is extremely small and amounts to about 0.1 fb. In this thesis, we present a resonant search for those two particles in their 3 Higgs boson decay in the kinematic regime in which the produced Higgs bosons are ultrarelativistic and, therefore, each pair of b jets from the decays is collimated. First, an analysis is given using Monte-Carlo simulation for the background and the expected values of the upper limits of the cross-section of the signal process are given. Due to the systematic disagreement of the data with the Monte-Carlo simulations, an alternative analysis is given where the background is estimated from the data. The data-driven background estimation method is explained in detail and the results of the method are given together with the results of statistical tests. In the end, the expected values of the upper limits for the cross-section of the signal process, obtained by the data-driven background estimation method, are given. Those expected upper limits on the cross-sections are of the order of 1 fb in mass regimes where each pair of b jets is collimated. In regimes where there is a high possibility of a b jet pair not being collimated, our analysis is not sensitive enough, and the expected upper limit increases by several orders of magnitude.