A parse tree (also called a DOM tree or document tree) is the hierarchical data structure produced when an HTML parser processes a web page's markup. The parser reads the raw HTML string and builds a tree of nodes representing the page's elements — the `<html>` root at the top, with `<head>` and `<body>` as immediate children, and all page content as nested descendants.
Each node in the parse tree represents an HTML element, a text node, or an attribute. The tree encodes the parent-child relationships between elements (nesting) and sibling relationships (elements at the same level). Navigating the parse tree allows scraping code to locate specific elements by traversing from the root down, jumping to a matching element, or walking up from a known element to access its parent or siblings.
Python's BeautifulSoup, JavaScript's Cheerio, and lxml all expose parse tree navigation through their APIs. Browser-based automation (Playwright, Puppeteer) operates on the live DOM tree rather than a parsed copy. Understanding the parse tree structure is essential for writing precise CSS selectors and XPath expressions that reliably locate target elements.