/usr/include/osgEarthDrivers/engine_quadtree/ is in libosgearth-dev 2.5.0+dfsg-8build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/osgEarthDrivers/engine_quadtree/Common
/usr/include/osgEarthDrivers/engine_quadtree/CustomPagedLOD
/usr/include/osgEarthDrivers/engine_quadtree/DynamicLODScaleCallback
/usr/include/osgEarthDrivers/engine_quadtree/FileLocationCallback
/usr/include/osgEarthDrivers/engine_quadtree/KeyNodeFactory
/usr/include/osgEarthDrivers/engine_quadtree/LODFactorCallback
/usr/include/osgEarthDrivers/engine_quadtree/QuadTreeTerrainEngineNode
/usr/include/osgEarthDrivers/engine_quadtree/QuadTreeTerrainEngineOptions
/usr/include/osgEarthDrivers/engine_quadtree/QuickReleaseGLObjects
/usr/include/osgEarthDrivers/engine_quadtree/SerialKeyNodeFactory
/usr/include/osgEarthDrivers/engine_quadtree/TerrainNode
/usr/include/osgEarthDrivers/engine_quadtree/TileModel
/usr/include/osgEarthDrivers/engine_quadtree/TileModelCompiler
/usr/include/osgEarthDrivers/engine_quadtree/TileModelFactory
/usr/include/osgEarthDrivers/engine_quadtree/TileNode
/usr/include/osgEarthDrivers/engine_quadtree/TileNodeRegistry