Good morning, My name is Carolina and would like to ask if it's possible to create a boundary line round a block entity?

I have trees on a drawing which are displayed as block entities. Once exploded they are shown as hatch entity, but there are several hatch areas for one single tree.

My aim is to rebuild the boundary of these trees to display them as polylines on Arcmap application, but having several hatch areas for each tree makes the rebuild boundary a very tedious task for all 30 trees on site.  

please check the attached images, before and after exploding the tree block

Is there a way of rebuilding a boundary for a block entity or how could I work around this so the task get more simple? Thank you