The Giving Trees are very unpredictable in what "bonus" you will get. I had one of my units die after collecting a "gift." Not sure they are viable in competitive play.
They're not and never were intended to be. They were originally something that players received from donating to the Giving Tree through PoxNora back in the days of Octopi. Later on the could be crafted from shards that you got from the old campaigns. Ever since the first revamp there's been no way to obtain them other than trading.