It's not possible to view a tree structure, but it is possible to create an asset numbering scheme that considers this need or depicts a hierarchy. I'm currently doing this by treating the asset type as a site (or property identifier). I also create an asset record for each type. I use a two-letter initial for client identification and a five digit number for the site's asset identifier. So for example, a asset type of PS-20101 represents Public Storage branch 20101 and PS-20102 represents branch 20102. Using the parent field (i.e., parent_id column in the assets data table), I create a site asset record for each type. This allows site buildings to be treated as sibling assets of a site.
In my case, I also have storage units associated with each building. So an Asset ID of PS-20101 might have 12 buildings numbered A-L. Thus, the asset records for PS-20101-A through PS-20101-L are assigned to the parent asset PS-20101. Individual storage units within those buildings are assigned a number with the parent asset beign the building asset. For example, PS-20101-D-201 is Storage Unit 201, located in Building D, which exists at site PS-20101. Individual storage units have doors and electrical circuits (systems), so this is handled in the asset number for those storage unit attributes (e.g., the door equipment asset id for PS-20101-D-201 is PS-20101-D-201-DOOR and the electrical circuit (system element) is PS-20101-D-201-ELECT.
Basically, you use the Parent field to create a hierarchy of assets with parent-sibling asset relationships. By using the parent field, you are basically creating a hierarchial tree.
Technically, CalemEAM can already handle the heirarchies--it just cannot display them because the existing grid does not support embedded tree widgets. The above solution uses a naming approach to mimic what cannot be displayed. However, it's probably possible to remedy this problem using one or more AJAX approaches in a modified version of the grid widget. Such approaches would probably minimize result list display times because the child assets of the upper-most parent assets could be shown or hidden using conventional AJAX approaches.