I already assign multiple 3d resources to a single task, now i wanna know if is possible to set the growth simulation in order to consider all my resources like a single one without create a single tree.
Synchro PRO 4.2 supports "Resource Groups" that allow you to do just what you described: treat selected resources as a single resource for the purpose of growth simulation without the need to merge the objects into single resource in the resource tree.
See the attached Help printout for directions to create Resource Groups. The growth simulation Appearance Profile can be assigned to the Resouce Group in Task Properties>Resource Groups
You should create and assign the Resource Group and unassign the Resources that were already assigned directly in Task Properties>Resources