It can be done by use of the Linework Code Set.
For a tree with canopy 15m diameter and trunk diameter of 0.8m I would use a code of "TREE 15 TR C.4"
TREE is in my description key set with the first parameter a scale parameter.
TR is in my Figure prefix database.
C is for circle in the Linework Code Set.
So as long as you only use the circle code for tree trunks it should be fine.
We have trees coded as TR 0.8 10 15. Where 0.8 is diameter, 10 is spread, 15 is height.
I have always found it much quicker not to shoot twice in the field but once then reduce the fieldwork data to csv or fbk then copy and paste the tree shots back into the csv or fbk and change there code to trunk. So effectively you have exactly the same points twice but with different codes. Then have a description key set up to bring in symbols based on the tree spread and trunk diameter. Works well.
Cheers
Ben