First Commit - Tree constructor

src/MultiSet.java

@@ -0,0 +1,29 @@
+import jdk.jshell.spi.ExecutionControl;
+public class MultiSet {
+
+    public static void add() throws Exception {
+        throw new Exception("Exception message");
+    }
+
+    public static void remove() throws Exception {
+        throw new Exception("Exception message");
+    }
+
+    public static void contains() throws Exception {
+        throw new Exception("Exception message");
+    }
+
+    public static void is_empty() throws Exception {
+        throw new Exception("Exception message");
+    }
+    public static void count() throws Exception {
+        throw new Exception("Exception message");
+
+    }
+
+    public static void size() throws Exception {
+        throw new Exception("Exception message");
+
+    }
+
+}

src/Tree.java

@@ -1,2 +1,25 @@
+import java.util.ArrayList;
+import java.lang.Object;
+
 public class Tree {
-}
+
+    //root of the tree
+    private Object root;
+    // list of all subtrees
+    private ArrayList<Tree> subtrees;
+
+    public Tree(Object root, ArrayList<Tree> subtrees){
+        this.root = root;
+        this.subtrees = subtrees;
+        if (subtrees.isEmpty()){
+            this.subtrees = new ArrayList<>();
+        }
+        else {
+            this.subtrees = subtrees;
+        }
+    }
+
+    public boolean is_empty(){
+        return this.root == null;
+    }
+}