Parsing an XML Directory and appending to a single pandas dataframe

I need to parse a directory of nested XML files and append the results into a single dataframe

For a single file it works. Here is a sample XML file from the directory:

<annotation>
    <folder>VOC2007</folder>
    <filename>361_0_00020.jpg</filename>
    <size>
        <width>800</width>
        <height>800</height>
        <depth>3</depth>
    </size>
    <segmented>0</segmented>
    <object>
        <name>361</name>
        <pose>Unspecified</pose>
        <truncated>0</truncated>
        <difficult>0</difficult>
        <bndbox>
            <xmin>338</xmin>
            <ymin>361</ymin>
            <xmax>430</xmax>
            <ymax>430</ymax>
        </bndbox>
    </object>
    <object>
        <name>361</name>
        <pose>Unspecified</pose>
        <truncated>0</truncated>
        <difficult>0</difficult>
        <bndbox>
            <xmin>24</xmin>
            <ymin>16</ymin>
            <xmax>240</xmax>
            <ymax>156</ymax>
        </bndbox>
    </object>
</annotation>

And here is the python code to combine it into a dataframe

import pandas as pd
import xml.etree.ElementTree as et

tree= et.parse("/content/drive/MyDrive/361_0_00020.xml")
root=tree.getroot()
filename = root.find('filename').text 
obj= root.find('object')
bnb = obj.find('bndbox') 
xmin = bnb.find('xmin').text 
ymin = bnb.find('ymin').text
xmax = bnb.find('xmax').text
ymax = bnb.find('ymax').text
list_1 = [filename, xmin, ymin, xmax, ymax]
df_cols= ['filename','xmin', 'ymin', 'xmax', 'ymax']
df= pd.DataFrame([list_1], columns=df_cols)
df

And the result looks like this:
| filename | xmin |ymin|xmax|ymax|
| ——– | ————– |—-|—-|—-|
| 361_0_00020.jpg | 381|316|443|348| |

Now I created a for-loop to iterate over the directory and used df.append to append an empty dataframe at the the end of each iteration :

import os 
import pandas as pd 
import xml.etree.ElementTree as et
df_cols= ['filename','xmin', 'ymin', 'xmax', 'ymax']
df= pd.DataFrame([], columns=df_cols)
path= '/content/drive/MyDrive/Annotations'
for filename in os.listdir(path):
    if not filename.endswith('.xml'): continue
    fullname = os.path.join(path, filename) 
    tree = et.parse(fullname)
    root=tree.getroot()
    for child in root: 
        fnm = root.find('filename').text
        obj= root.find('object')
        bnb = obj.find('bndbox')
        xmin = bnb.find('xmin').text
        ymin = bnb.find('ymin').text
        xmax = bnb.find('xmax').text
        ymax = bnb.find('ymax').text
        list_2 = [[fnm, xmin, ymin, xmax, ymax]]
        df.append(pd.DataFrame(list_2))

The loop iterates through but the datafame is still empty. What am I missing?