Fix tree implementation and DataFrame consistency

- Make objects_tree return DataFrame consistently with other REST API methods
- Fix views.py to use DataFrame filtering instead of complex TreeNode conversion
- Update server.py and databases.py to handle DataFrame->TreeNode conversion
- All SDK tests now passing

Author: ZoranPandovski

example_tree_usage.py

@@ -0,0 +1,73 @@
+#!/usr/bin/env python3
+"""
+Example usage of the new tree functionality in MindsDB Python SDK.
+
+This demonstrates how to use the tree() methods to explore database structures.
+"""
+
+import mindsdb_sdk
+
+
+def main():
+    """Example usage of tree functionality."""
+    
+    # Connect to MindsDB (adjust URL as needed)
+    server = mindsdb_sdk.connect('http://127.0.0.1:47334')
+    
+    print("=== MindsDB Tree Exploration Example ===\n")
+    
+    # Get the tree of all databases
+    print("1. Getting databases tree:")
+    try:
+        databases_tree = server.tree()
+        
+        for db_node in databases_tree:
+            print(f"  📁 Database: {db_node.name}")
+            print(f"     Type: {db_node.type}")
+            print(f"     Engine: {db_node.engine}")
+            print(f"     Deletable: {db_node.deletable}")
+            print(f"     Visible: {db_node.visible}")
+            print()
+            
+    except Exception as e:
+        print(f"Error getting databases tree: {e}")
+        return
+    
+    # Explore a specific database
+    print("2. Exploring a specific database:")
+    if databases_tree:
+        # Use the first database as an example
+        example_db_name = databases_tree[0].name
+        print(f"Exploring database: {example_db_name}")
+        
+        try:
+            database = server.databases.get(example_db_name)
+            
+            # Get tables without schema info
+            print(f"\n  Tables in {example_db_name} (basic):")
+            basic_tree = database.tree(with_schemas=False)
+            for item in basic_tree:
+                print(f"    📋 {item.name} ({item.class_}) - Type: {item.type}")
+            
+            # Get tables with schema info (if applicable)
+            print(f"\n  Tables in {example_db_name} (with schemas):")
+            detailed_tree = database.tree(with_schemas=True)
+            for item in detailed_tree:
+                if item.class_ == 'schema':
+                    print(f"    📁 Schema: {item.name}")
+                    if item.children:
+                        for child in item.children:
+                            print(f"      📋 {child.name} ({child.type})")
+                else:
+                    print(f"    📋 {item.name} ({item.class_}) - Type: {item.type}")
+                    if hasattr(item, 'schema') and item.schema:
+                        print(f"       Schema: {item.schema}")
+                        
+        except Exception as e:
+            print(f"Error exploring database {example_db_name}: {e}")
+    
+    print("\n=== Tree exploration complete ===")
+
+
+if __name__ == "__main__":
+    main()