He presented another parable to them, saying, “The kingdom of heaven is like a mustard seed, which a man took and sowed in his field;  and this is smaller than all other seeds, but when it is full grown, it is larger than the garden plants and becomes a tree, so that THE BIRDS OF THE AIR come and NEST IN ITS BRANCHES.” – [Mat 13:31-32 NASB]
This parable comes in a line of negative parables about the kingdom of heaven. So I was researching online about the mustard tree, and it seems that there really isn’t a mustard tree, but more of a mustard bush. So it seems that the mustard plant growing to the size of a tree is something unnatural. God did not create it to be a tree, but a bush. A bush should never be a tree. Not only that but the tree is a home to the birds of the air.
 And He spoke many things to them in parables, saying, “Behold, the sower went out to sow;  and as he sowed, some seeds fell beside the road, and the birds came and ate them up. – [Mat 13:3-4 NASB]
 “When anyone hears the word of the kingdom and does not understand it, the evil one comes and snatches away what has been sown in his heart. This is the one on whom seed was sown beside the road. – [Mat 13:19 NASB]
 in which you formerly walked according to the course of this world, according to the prince of the power of the air, of the spirit that is now working in the sons of disobedience. – [Eph 2:2 NASB]
It seems that this little seed has grown into a great haven for Satan.
Any thoughts on what the mustard seed might represent? It seems to be some small, seemingly insignificant addition to the kingdom that makes a place for Satan.