A few people have been asking whether the money tree aspiration reward from the Sims 4 Seasons expansion is allowed in the Legacy Challenge. Pinstar has decided to not allow the use of this aspiration reward as it can be extremely powerful (in that yours Sims can get a lot of simoleons easily). The rules have been updated to reflect this change. You can purchase the reward if you want, you just can’t use it (much like the elixer of life in Sims 2).
Thank you to those of you who have pointed this out to us. We actually hadn’t used the money tree yet and were unaware of this.