The scene tree holds information about how the level looks (graphics, particle effects etc), the geometry (solid things) and other physics-related items (like gravity and wind) that affect the Goo Balls.

The Scene Root item has a few properties of its own. Full Details Here

Scene Bound : minx,maxx,miny,maxy

These four values define the visual scene bounds - how far the level can be scrolled. No part of the level outside this area will ever be displayed on screen. Placing essential items (like the exit) outside these bounds could mean your level is unplayable. Placing balls outside this area is highly discouraged, since you won't be able to see them, or pick them up.

See also [Scene Bounds vs autobounds=true]

The Scene Tree contains....