One or more systems and/or techniques for generating an adaptive tree structure for storing event data based upon data density of events are disclosed. In particular, the adaptive tree structure may comprise one or more levels of nodes, where a level may correspond to a resolution of events. Nodes may correspond to particular time spans over which event data was recorded. A node may be designated as a raw node comprising raw events or a summary node comprising summary events based upon the number of events occurring within a time span covered by the node.