When the roots of this mighty tree are reaching Fishman Island, then there has to be a tree on the surface! And there is the Holy Land of Mary Geosie with its mighty walls.
These high walls of Mary Geoise are hiding this big tree. We are talking about Uranus -> the devil fruit tree! Which is the National Treasure.
That’ why the Celestial Dragons have such a power over the Marines and the World Government. Because they are in possession of Uranus and have the monopoly of devil fruits and provide them with it (like the devil fruit presents for CP9)
But over the time of hundreds of years, devil fruit users died and the devil fruits got reborne into the world and fall into the hand of pirates.
“Doflamingo said “the power is decreasing and it rots away!”
This can mean, that the devil fruit tree have problems to provide the World Government and Marines with devil fruits. What do you guys think?
*Theory by Wolfram87