If the tree Block is one ordinary Block, then while you can vary the height easily enough with the Z scale of each insertion, the trunk diameter and canopy size, set by the X and Y scale factors, will always have the same relationship to each other.  That is, one insertion won't be able to have, say, twice the trunk diameter of another one but three times its canopy size.  If you want to specify each tree's trunk diameter and the canopy size separately, I think you're going to need one Block for the trunk and a different one for the canopy.  But you could at least Group them together to keep each tree as, in a sense, "one" thing.  [I'm not familiar enough yet with Dynamic Blocks to know whether they can get you around this issue.]

Edited by Kent Cooper - 19.May.2014 at 15:15

I guess he isn't going to share.  Makes me wonder if he ever had such a block to begin with.