diff --git a/include/tree.h b/include/tree.h
new file mode 100644
index 0000000..321dc99
--- /dev/null
+++ b/include/tree.h
@@ -0,0 +1,76 @@
+#ifndef LIBABACUS_TREE_H
+#define LIBABACUS_TREE_H
+
+#include "libabacus.h"
+#include "vec.h"
+
+/**
+ * Enum to represent the variant of a tree node.
+ */
+enum tree_variant {
+    NONE,
+    BASE,
+    ID,
+    STR,
+    CHAR,
+    NUM,
+    BOOL,
+    KW,
+    OP,
+    UNARY_OP,
+    BLOCK,
+    FUN,
+    IF,
+    WHILE,
+    DOWHILE,
+    FOR,
+    CALL,
+    RETURN
+};
+
+/**
+ * A tree node that has been parsed from the input tokens.
+ */
+struct tree {
+    /**
+     * The variant of tree node.
+     */
+    enum tree_variant variant;
+    /**
+     * The string value of this tree, if applicable.
+     */
+    char* string_value;
+    /**
+     * The int value of this tree, if applicable.
+     */
+    int int_value;
+    /**
+     * The children of this tree node. This vector
+     * will not be initialized if this tree node
+     * type does not usually have children.
+     */
+    vec children;
+
+    /**
+     * The line on which this tree starts.
+     */
+    size_t line;
+    /**
+     * The index in the string where this line begins.
+     */
+    size_t line_from;
+    /**
+     * The beginning in the string of this tree.
+     */
+    size_t from;
+    /**
+     * The index in the string of the next
+     * thing that isn't part of this tree.
+     */
+    size_t to;
+};
+
+typedef enum tree_variant tree_variant;
+typedef struct tree tree;
+
+#endif