Ann even if you wanted to look at the mustard "tree," it's still in a negative context, because as Jerome pointed out the birds have been allowed to settle in.
The whole context of Matthew 13 is talking about the offer of the kingdom. It starts out as an offer to the nation of Israel, and then after it is rejected it is offered to a new entity. And then it progresses through how the teaching is corrpupted throughout time. So even with it being a "tree" the context still doesn't lend itself to a positive reading.
Further context throughout Scripture supports this.
The whole context of Matthew 13 is talking about the offer of the kingdom. It starts out as an offer to the nation of Israel, and then after it is rejected it is offered to a new entity. And then it progresses through how the teaching is corrpupted throughout time. So even with it being a "tree" the context still doesn't lend itself to a positive reading.
Further context throughout Scripture supports this.