Tree component example:
```jsx static
import React from 'react';
import { Panel } from 'polestar-ui-kit';

class MyComponent extends React.Component {

    render() {
        return (
            <Panel
                icon="bar-chart-o"
                title="제목"
                collapsible={false}
                menu={{
                    items: [
                        { label: 'item1', value: '1' },
                        { label: 'item2', value: '2' },
                        { label: 'item3', value: '3' },
                        { label: 'item4', value: '4' },
                        { label: 'item5', value: '5' },
                    ],
                    onItemClick: this.onPanelMenuItemClick,
                }}
                headerHeight={40}
                headerColor="red"
                customButtons={[
                    <Button>btn1</Button>,
                    <Button>btn2</Button>,
                    <Button>btn3</Button>,
                ]}
                contentHeight={100}
                footer={<div>Footer 영역</div>}
            >
                Content 영역
            </Panel>
        );
    }
}

export default MyComponent;
```