Run a loop with a variable counter 50
While counter > 0
Pick random spot
If spot is NOT within minimum of distance of tree - Place tree at spot, reduce counter by 1
(if it is too close to a placed tree, the event will run again without reducing the counter and pick a new spot to try)
Edit: Depending on the availability of space for placement, this can be a very inefficient method. If there is not much space left for that last tree, it might loop a ton of times before randomly hitting that spot.