diff --git a/specs/tri/trees/tree.t27 b/specs/tri/trees/tree.t27
index 10b42db80f..1a571ca818 100644
--- a/specs/tri/trees/tree.t27
+++ b/specs/tri/trees/tree.t27
@@ -22,66 +22,112 @@ module TriTree;
     // ═══════════════════════════════════════════════════════════
 
     // leaf(value: T) → void
-    fn leaf(value: T) -> void {
-        // TODO: Implement from .tri spec
+    fn leaf(value: T) -> Tree(T) {
+        // Create a leaf tree with the given value
+        let tree = Tree(T) {
+            is_leaf: true,
+            value: value,
+            left: undefined,
+            right: undefined,
+        };
+        return tree;
     }
 
     // branch(left: Tree(T)) → void
-    fn branch(left: Tree(T)) -> void {
-        // TODO: Implement from .tri spec
+    fn branch(left: Tree(T), right: Tree(T)) -> Tree(T) {
+        // Create a branch tree with the given left and right subtrees
+        let tree = Tree(T) {
+            is_leaf: false,
+            value: undefined,
+            left: left,
+            right: right,
+        };
+        return tree;
     }
 
     // is_leaf(tree: Tree(T)) → void
-    fn is_leaf(tree: Tree(T)) -> void {
-        // TODO: Implement from .tri spec
+    fn is_leaf(tree: Tree(T)) -> bool {
+        // Return whether the tree is a leaf node
+        return tree.is_leaf;
     }
 
     // height(tree: Tree(T)) → void
-    fn height(tree: Tree(T)) -> void {
-        // TODO: Implement from .tri spec
+    fn height(tree: Tree(T)) -> usize {
+        // Return the height of the tree (number of edges from root to deepest leaf)
+        if tree == undefined {
+            return 0;
+        }
+        if tree.is_leaf {
+            return 0;
+        }
+        let left_height = height(tree.left);
+        let right_height = height(tree.right);
+        return 1 + max(left_height, right_height);
     }
 
     // size(tree: Tree(T)) → void
-    fn size(tree: Tree(T)) -> void {
-        // TODO: Implement from .tri spec
+    fn size(tree: Tree(T)) -> usize {
+        // Return the number of nodes in the tree
+        if tree == undefined {
+            return 0;
+        }
+        if tree.is_leaf {
+            return 1;
+        }
+        let left_size = size(tree.left);
+        let right_size = size(tree.right);
+        return 1 + left_size + right_size;
     }
 
     // inorder(tree: Tree(T)) → void
-    fn inorder(tree: Tree(T)) -> void {
-        // TODO: Implement from .tri spec
+    fn inorder(tree: Tree(T)) -> []T {
+        // Return the values of the tree in inorder traversal (left, root, right)
+        if tree == undefined {
+            return [];
+        }
+        if tree.is_leaf {
+            return [tree.value];
+        }
+        let left_values = inorder(tree.left);
+        let right_values = inorder(tree.right);
+        return left_values + [tree.value] + right_values;
     }
 
     // ═══════════════════════════════════════════════════════════
     // TDD: Tests (from .tri behaviors)
     // ═══════════════════════════════════════════════════════════
 
-    test leaf_basic_case
+    test "leaf_basic_case"
         given input = default_input()
         when result = leaf(input)
-        then result != undefined
-
-    test branch_basic_case
-        given input = default_input()
-        when result = branch(input)
-        then result != undefined
-
-    test is_leaf_basic_case
+        then result.is_leaf == true
+        then result.value == input
+
+    test "branch_basic_case"
+        given left = default_input()
+        given right = default_input()
+        when result = branch(left, right)
+        then result.is_leaf == false
+        then result.left == left
+        then result.right == right
+
+    test "is_leaf_basic_case"
         given input = default_input()
         when result = is_leaf(input)
-        then result != undefined
+        then result == true
 
-    test height_basic_case
+    test "height_basic_case"
         given input = default_input()
         when result = height(input)
-        then result != undefined
+        then result >= 0
 
-    test size_basic_case
+    test "size_basic_case"
         given input = default_input()
         when result = size(input)
-        then result != undefined
+        then result >= 1
 
-    test inorder_basic_case
+    test "inorder_basic_case"
         given input = default_input()
         when result = inorder(input)
-        then result != undefined
+        then len(result) >= 1