Sanguis

This tree, at first sight, appears bright, lush, and tempting. Sweet, plump fruits line its branches and it almost seems to sing to onlookers. Leaves are a soft beautiful green that entices those looking for respite. It calls to them, beacons to them. It tempts them to come close and taste of its fruits and feel the sweet embrace of its soft leaves.

In reality, this tree is the result of a dragon using blood magic to better himself with stalwart wood, trying to make scale and flesh even more impenetrable. The result was a seething and oozing amalgamation of pulsating flesh, blood, wood-like structure and bone. The entire skeleton of the dragon is melded into the trunk. The claw of each leg is reaching out with outstretched talons, as if the spirit of the dragon is still trying to scrape out of the now tainted prison of its own body. As if it still feels the pain of exposed bone and muscle. The skull of the dragon, still moist with flesh, is gaping wide as if in a throat-rending scream. The wings stretch straight up and then out, creating an illusion of a leafy canopy. The membrane no longer a leathery blanket but a twisting web of branch-like structures spreading out in every direction, covered in hundreds of fangs, claws, and spines.

These branch-like structures move like vines, swiftly piercing victims where they are soft and uncovered with scale, tearing them apart from the inside out and drinking their blood. These "trees" collect and use the leftover bones, fangs and talons to add yet more "branches" to it's canopy and grow in size. Some of the more ancient ones are known to be able to reduce even the biggest and strongest of dragons to bone and scale in seconds.

Every once in a while, instead of consuming, these will take over the mind of a victim by rupturing the brain. It will create a drone out of the dragon and prime its body to find a new location and plant itself to become a new "yggdrasil".

I feel like your lair might specifically take care of it and "feed" it with traitors, somehow priming the rest so that it doesn't attack who they don't want it to.

I feel someone like Nicholai can figure out how to "tame" it like that.