MongoDB Documentation, Release 3.0.4 Model Tree Structures with Parent References Overview Pattern 4.3. Data Model Examples and Patterns 157 Data in MongoDB has a flexible schema . Collections do not enforce document structure. Decisions that affect how you model data can affect application performance and database capacity. See Data Modeling Concepts (page 145) for a full high level overview of data modeling in MongoDB. This document describes a data model that describes a tree-like structure in MongoDB documents by storing references (page 147) to “parent” nodes in children nodes. The Parent References pattern stores each tree node in a document; in addition to the tree node, the document stores the id of the node’s parent. Consider the following hierarchy of categories: The following example models the tree using Parent References , storing the reference to the parent category in the field parent : db.categories.insert( { _id: "MongoDB", parent: "Databases" } ) db.categories.insert( { _id: "dbm", parent: "Databases" } ) db.categories.insert( { _id: "Databases", parent: "Programming" } ) db.categories.insert( { _id: "Languages", parent: "Programming" } )