A combined viewer-spreadsheet application provides display of (i) a spreadsheet including a tree window for an extendable tree structure of an object and (ii) a three dimensional (3D) model of the object. A user of the application is able to add one or more columns or arrays to the tree structure and to reflect in the 3D model the values of elements of the columns or arrays added. The tree structure includes at least one assembly, a plurality of subassemblies forming the assembly, and a plurality of parts for each of the subassemblies.