added initial tree

src/Tree.java

@@ -1,2 +1,23 @@
+import java.util.ArrayList;
+
 public class Tree {
+
+    /**
+     * A recursive tree data structure, which provides services required of the
+     * MultiSet ADT. See TreeMultiSet, which is the next class defined.
+     * This is a simplified version of the Tree data structure
+     * adapted from CSC148.
+     */
+
+    // The item stored at this tree's root, or null if empty.
+    private Object root = null;
+    // The list of all subtrees of this tree.
+    private ArrayList<Tree> subtrees;
+
+    public Tree(Object root, ArrayList<Tree> subtrees) {
+        this.root = root;
+        if (root == null) {
+            this.subtrees = new ArrayList<>();
+        } else this.subtrees = new ArrayList<>(subtrees);
+    }
 }