Elastic Search Nested Aggregations

[onlinejava]

Hi
i am new to elastic search Query and aggregation.
I have a nested document with the following mapping

PUT /company
{
"mappings": {
"data": {
"properties": {
"deptId": {
"type": "keyword"
},
"deptName": {
"type": "keyword"
},
"employee": {
"type": "nested",
"properties": {
"empId": {
"type": "keyword"
},
"empName": {
"type": "text"
},
"salary": {
"type": "float"
}}
} } } }}

I have sample data like

PUT company/data/1
{
"deptId":"1",
"deptName":"HR",
"employee": [
{
"empId": "1",
"empName": "John",
"salary":"1000"
},
{
"empId": "2",
"empName": "Will",
"salary":"2000"
}
]
}

PUT company/data/2
{
"deptId":"2",
"deptName":"FINANCE",
"employee": [
{
"empId": "1",
"empName": "John",
"salary":"1000"
}]
}

PUT company/data/3
{
"deptId":"3",
"deptName":"FINANCE",
"employee": [
{
"empId": "1",
"empName": "John",
"salary":"1000"
},
{
"empId": "2",
"empName": "Will",
"salary":"2000"
},
{
"empId": "3",
"empName": "Mark",
"salary":"4000"
}]
}

I would like assisting in creating a Query to

1. Department with the maximum Employees
2. Employee that is present in most departments